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ECONOMIC    DISPOSAL    OF   TOWN'S    REFUSE. 

A  work  dealing  most  exhaustively  with  the  problem  of  Towns'  Refuse 
Disposal.  Gives  a  description  of  the  various  types  of  Dust  Destructors 
which  have  been  erected,  with  results  of  their  working.  By  W.  FRANCIS 
GOODRICH,  A.I.Mech.E.  Demy  8vo,  Cloth,  numerous  Illustrations. 
IDS.  6rf.  net. 

Public  Health  Engineer. — "A  most  valuable  work  of  reference,  as  well  as  an  instruc- 
tive treatise  on  a  most  important  branch  of  sanitary  engineering.  A  book  which  no 
municipal  engineer  or  cleansing  superintendent  can  afford  to  be  without." 

ELEMENTS    OF    STATISTICS. 

By  ARTHUR  L.  BOWLEY,  M.A.,  F.S.S.,  Lecturer  in  Statistics  at  the  London 
School  of  Economics.  Demy  8vo,  Cloth,  342  pp.  Numerous  Diagrams. 
IDS.  6d.  net. 

This  book  is  intended  to  supply  a  text -book  dealing  with  the  methods  and  principles 
of  Statistics  recognised  or  used  by  Official  Statisticians.  To  Public  Officials,  Town  Clerks, 
Medical  Officers,  Accountants  and  others  engaged  in  Municipal  and  I^ocal  Government, 
this  book  will  be  especially  useful. 

THE    SANITARY    INSPECTOR'S    GUIDE. 

A  Text-book  on  the  Public  Health  Act,  1875,  and  the  Public  Health  Acts 
Amendment  Act,  1890,  so  far  as  they  affect  the  Inspector  of  Nuisances. 
By  H.  LEMMOIN-CANNON,  Professional  Associate  Surveyors'  Institution, 
Associate  Sanitaiy  Institute,  &c,,  &c.  Cr.  8vo,  Cloth,  256 pp.  35.  6d.  net. 

PUBLIC    HEALTH    AND    HOUSING. 

The  Influence  of  the  Dwelling  upon  Health  in  Relation  to  the  Changing 
Style  of  Habitation.  By  JOHN  J.  F.  SYKES,  M.D.,  D.Sc.  (Edin.),  Medical 
Officer  of  Health,  St.  Pancras,  &c.  Cr.  8vo,  Cloth.  55.  net. 

THE    COTTAGE    HOMES    OF    ENGLAND. 

The  Case  Against  the  Housing  System  in  Rural  Districts.  By  W. 
WALTER  CROTCH.  Second  Edition,  Revised  and  Enlarged.  Cr.  8vo, 
Cloth.  2S.  net. 


SEWAGE    WORKS    ANALYSES 


SEWAGE  WORKS 
ANALYSES 


BY 


GILBERT  J.  FOWLER,  M.Sc.  (Vici.)  F.I.C. 

Superintendent  and  Chemist,  Manchester  Corporation 
Sewage  Works 


JOHN   WILEY  &   SONS 
EAST  NINETEENTH   STREET 

:   p.   s.   KING  &  SON 
1902 


BRADBURY,   AGNEW,   &  CO.   LD.,   PRINTERS, 
LONDON   AND  TONBRIDGE. 


PREFACE. 


THE  following  book  has  been  written  in 
response  to  several  requests  for  an  account  of 
the  methods  of  analysis  in  use  in  the  labora- 
tory of  the  Manchester  Corporation  Sewage 
Works. 

Through  the  courtesy  of  Mr.  F.  Scudder,  the 
author  has  also  been  able  to  include  descrip- 
tions of  some  of  the  more  important  processes 
employed  in  the  laboratory  of  the  Mersey  and 
Irwell  Joint  Committee. 

In  general,  it  may  be  said  that  the  Joint 
Committee's  methods  are  designed  for  cases 
where  samples  from  different  works  have  to  be 
critically  examined,  the  Manchester  methods 
for  the  analysis  of  a  large  number  of  samples 
of  sewage  and  effluents  of  the  same  general 
character. 

The  successful  application  of  modern  bac- 
terial processes  will  necessitate  careful  chemical 
control.  It  is  hoped,  therefore,  that  the  follow- 
ing book  will  prove  of  use  to  the  increasing 


vi  PREFACE. 

number  of  chemists  who  are  interested  in  the 
scientific  treatment  of  sewage. 

The  methods  here  described  are  such  as 
a  considerable  experience  has  shown  to  be 
capable  of  being  rapidly  executed,  and  of 
giving  results  of  an  accuracy  amply  sufficient 
for  practical  requirements. 

In  conclusion,  the  author  wishes  to  express 
his  indebtedness  to  the  scientific  advisers  of 
the  Royal  Commission  on  Sewage  Disposal 
for  many  helpful  suggestions. 


TABLE  OF  CONTENTS. 


CHAP.  PAGE 
I.      THE     CHEMICAL     CONTROL    OF     SEWAGE     PURI- 
FICATION   PROCESSES     I 

II.      THE     DETERMINATION    OF   ABSORBED    OXYGEN    .      21 

III.  THE    DETERMINATION    OF   AMMONIA    .  .  .38 

IV.  THE        DETERMINATION       OF       NITRITES       AND 

NITRATES 6l 

V.      THE    DETERMINATION    OF   DISSOLVED    OXYGEN    .      75 

VI.      THE     DETERMINATION     OF    CHLORINE,     ACIDITY 

AND   ALKALINITY,   AND    IRON    COMPOUNDS        .      86 

VII.       THE    DETERMINATION  OF   SOLIDS    IN    SOLUTION 

AND  SUSPENSION IOI 

VIII.      THE     ANALYSIS     OF     GASES     FROM     THE     SEPTIC 

TANK   AND    FROM    BACTERIAL   FILTERS  .  .112 


TABLE      I.      ATOMIC   WEIGHTS       .  .  .  .  .126 

TABLE    II.      THE    METRIC    SYSTEM          .  .  .  .127 

TABLE  III.  CONVERSION  TABLE — GRAINS  PER  GALLON, 
QUANTITY  IN  ONE  MILLION  GALLONS, 
PARTS  PER  IOO,OOO  .  .  .  .128 

TABLE  IV.  CONVERSION  TABLE  FOR  RECORDING 
QUANTITY  OF  SEWAGE  DEALT  WITH 
PER  GIVEN  AREA  ....  I2Q 

USEFUL   DATA 13! 


or  THE 

•      ';•••<? 


SEWAGE  WORKS  ANALYSES, 


CHAPTER  I. 

THE   CHEMICAL   CONTROL    OF   SEWAGE 
PURIFICATION   PROCESSES. 

THE  efficiency  of  any  process  of  sewage  purifi- 
cation is  measured  by  the  difference  between  the 
impurities  in  the  liquid  before  and  after  the  process 
in  question. 

For  the  most  part  the  amount  of  impurity 
present  can  only  be  accurately  determined  by 
chemical  analysis,  although  valuable  information 
can  be  obtained  from  the  physical  characters  of 
the  liquid,  such  as  its  colour,  opacity,  smell,  etc. 

Chemical  analysis  is  in  all  cases  necessary  in 
order  to  determine  whether  an  effluent  is  suffi- 
ciently purified  to  enter  a  stream,  as  it  may  often 
be  free  from  smell  or  from  matters  in  suspension, 
and  yet  contain  much  impurity  in  solution  which 
will  develop  putrefaction  later  on. 

The  chief  sewage  treatment  processes  in  practical 
operation  may  be  broadly  divided  into  two  classes — 

(a)  Mechanical  or  Disposal  Processes. 

(b)  Biological  or  Purification  Processes. 

S.W.  B 


2  SEWAGE  WORKS  ANALYSES. 

(a)  Mechanical  Processes. — Under  this  head  would 
be  classed  such  methods  as  the  removal  of  garbage 
and  detritus  by  catch-pits  and  screens,  and  the 
settling  out  of  suspended  matters  in  detritus  or 
sedimentation  tanks. 

The  process  of  chemical  precipitation  is  to  a  large 
extent  mechanical,  the  precipitate  produced  by 
the  chemicals  used  (in  general,  lime,  sulphate  of 
alumina,  or  lime  and  copperas)  dragging  down 
the  lighter  suspended  matters  and  leaving  a  clear 
effluent. 

A  certain  amount  of  true  chemical  action  may 
also  take  place  when  chemicals  are  added,  e.g., 
the  formation  of  carbonate  of  lime  by  interaction 
of  the  lime  with  the  carbonic  acid  and  carbo- 
nates of  the  sewage,  the  neutralisation  by  lime 
of  the  acids  present  in  manufacturing  sewage, 
the  combination  of  the  hydrates  of  iron  and 
aluminium  with  dyes  and  other  partially  soluble 
impurities. 

The  total  of  the  impurities  present  is,  however,  un- 
altered by  ordinary  chemical  treatment ;  the  grosser 
solids  and  fine  flocculent  suspended  matters  are 
coagulated  by  the  chemicals  and  precipitated  as 
sludge,  while  the  substances  actually  in  solution 
pass  away  in  the  effluent,  and  unless  the  chemicals 
have  been  added  in  such  quantities  as  to  sterilise 
the  latter,  these  impurities  will  undergo  putrefac- 
tion, if  the  necessary  conditions  arise. 

Another  process  which  may  be  mentioned  here 
is  mechanical  filtration. 


SEWAGE   WORKS  ANALYSES.  3 

Many  forms  of  mechanical  filters  have  been 
devised,  and  to  some  extent  made  use  of,  their 
chief  function  being  to  arrest  any  suspended 
matter  which  may  have  escaped  removal  by  settle- 
ment or  chemical  treatment. 

(b)  Biological  Purification  Processes. — The  pro- 
cesses mentioned  in  the  foregoing  paragraph  are 
not  strictly  speaking  sewage  purification  processes, 
inasmuch  as  the  impurities  removed  are  not 
destroyed,  but  only  collected  together,  so  as  to 
be  more  conveniently  disposed  of;  e.g.,  the  garbage 
from  screens  requires  to  be  burnt  or  tipped,  the 
sludge  from  settling  tanks  must  be  pressed  into 
cakes,  dried  in  lagoons,  or  sent  away  to  sea  in  the 
liquid  state.  By  biological  processes  alone  is 
there  true  purification. 

These  processes  make  use  of  the  micro-organisms 
originally  present  or  capable  of  development  in 
the  sewage  to  altogether  change  the  organic 
impurities  in  the  sewage  and  convert  them  into 
harmless  inorganic  substances. 

In  the  septic  tank  the  changes  which  take  place 
are  chiefly  brought  about  by  so-called  anaerobic 
organisms  which  are  active  in  absence  of  air.  By 
the  activity  of  these  organisms  much  of  the  solid 
impurity  in  the  sewage  is  liquefied  and  converted 
into  gas,  and  the  substances  in  solution  are  altered 
and  broken  down  in  such  a  way  as  to  render  them 
more  easily  attacked  by  another  class  of  organisms, 
which  are  active  in  presence  of  oxygen  or  air,  and 
which  are  developed  in  the  soil  (in  the  case  of  land 

B  2 


4  SEWAGE   WORKS  ANALYSES. 

filtration),   or  in  the  various  forms  of  bacterial 
filters. 

Under  certain  circumstances  it  may  be  possible 
to  apply  crude  sewage  directly  to  land  or  to 
bacterial  filters,  but  in  these  cases  the  amount 
which  can  be  purified  per  given  area  is  much 
less  than  when  some  preliminary  treatment  is 
used. 

In  some  cases  a  combination  of  mechanical  and 
biological  treatment  may  be  made  use  of,  e.g., 
when  the  effluent  from  sedimentation  tanks  or  from 
chemical  treatment  is  applied  to  bacterial  filters  or 
to  land. 

Of  bacterial  filters  there  are  two  types,  the 
contact  bed  and  the  continuous  filter. 

In  the  case  of  the  contact  bed  the  sewage  or 
tank-effluent  is  allowed  to  run  on  till  the  bed  is 
full ;  it  is  held  in  contact  for  a  given  time,  after 
which  the  bed  is  discharged  and  allowed  to  rest 
empty  for  a  certain  period. 

Continuous  filters  are  usually  constructed  of 
greater  depth  and  with  coarser  material  than 
contact  beds,  and  the  sewage  is  delivered  upon 
them  in  a  continuous  shower  by  various  forms  of 
sprinkling  apparatus. 

The  changes  which  take  place  in  all  these  pro- 
cesses are  much  more  complex  than  those  which 
are  effected  by  any  of  the  mechanical  or  disposal 
methods  in  class  (#),  and  chemical  control  is  abso- 
lutely necessary  if  they  are  to  be  maintained  at 
their  greatest  efficiency. 


SEWAGE  WORKS   ANALYSES. 


THE   GAUGING   OF   SEWAGE   FLOW. 

In  order  accurately  to  estimate  the  work  done 
by  any  of  the  foregoing  processes  it  is  necessary 
that  the  volume  of  sewage  dealt  with  should  be 
known  as  exactly  as  possible. 

The  gauging  of  large  volumes  of  water  belongs 
to  the  province  of  the  engineer,  but  it  is  essential 
that  the  chemist  should  be  acquainted  with  the 
chief  methods  in  use  for  this  object. 

A  rough  estimate  of  the  quantity  of  sewage 
entering  a  works  in  dry  weather  may  be  made 
when  the  population  connected  with  the  sewers  is 
known,  a  certain  quantity  per  head  being  allowed, 
and  a  further  estimate  being  made  for  trade 
effluents.  It  is  obvious,  however,  that  the  quantity 
per  head  will  vary  very  much  according  to  the 
water  supply,  the  character  of  the  manufactures 
carried  on,  the  state  of  trade,  etc.  In  towns  with 
old  and  leaky  sewers  much  subsoil  water  often 
enters,  and  thus  interferes  with  an  accurate 
estimate. 

It  is  necessary  therefore  to  actually  measure  the 
quantity  of  sewage  delivered.  This  is  accomplished 
by  means  of  various  forms  of  recording  gauges, 
e.g.,  Bailey's  Sewage  Recorder,  or  the  Palatine 
Company's  Recording  Gauge.  The  principle  of 
these  instruments  is  similar,  viz.,  the  motion  of 
a  float,  which  rises  and  falls  with  the  sewage, 
is  recorded  by  a  pen  on  a  revolving  drum 
worked  by  a  clock.  A  tracing  is  thus  obtained 


6  SEWAGE   WORKS   ANALYSES. 

giving  the  height  of  the  sewage  at  any  hour  of 
the  day. 

The  rates  of  flow  corresponding  to  these  heights 
are  obtained  from  engineering  tables  which  are 
worked  out  from  different  formulae  according  to 
the  conditions  under  which  the  measurement 
is  made. 

The  flow  may  thus  be  measured  : — 

(a)  In  a  sewer  of  known  dimensions  and  fall. 

(b)  Over  a  V  notch  leading  from  a  still  body  of 

liquid. 

(c)  Over  a  rectangular  weir  of  known  dimensions 

discharging  over  a  thin  edge  from  a  still 
body  of  liquid. 

(d)  In  a  rectangular  channel  of  known  dimen- 

sions and  fall,  and  with  a  free  exit. 

For  the  formulae  and  tables  necessary  to  calcu- 
late the  flow  under  these  conditions,  engineering 
works  should  be  consulted,  e.g. — 

"Memorandum  of  Formulas  and  Tables  of 
Velocities  and  Discharges  of  Sewers,"  T.  de 
Courcy  Meade,  City  Surveyor,  Manchester. 

"  Sanitary  Engineering,"  Lt.-Col.  Moore, 
Chaps.  III.,  IV.  and  V. 

"  Tables  and  Diagrams  for  use  in  designing 
Sewers  and  Water  Mains,"  W.  Santo  Crimp  and 
C.  Ernest  Bruges. 

"Flow  of  Water,"  Ganguillet  and  Kutter, 
translated  into  English  by  Rudolph  Hering  and 
J.  C.  Trau twine. 

The  records  obtained  by  such  methods  as  the 


FIG.  i.-KENT'S   METER   FOR   MEASURING 
DISCHARGE   FROM   BACTERIA   BEDS. 


[To  face  page  7. 


SEWAGE   WORKS  ANALYSES.  7 

above  may  be  usefully  checked  by  noting  the  time 
which  a  tank  of  known  dimensions  takes  to  fill  at 
different  periods  of  the  day. 

In  cases  where  the  above  methods  cannot  con- 
veniently be  used  owing  to  the  absence  of  the 
necessary  fall,  e.g.,  when  measuring  the  discharge 
from  filters,  a  meter  which  will  work  under  a  low 
head  of  water  must  be  used. 

Such  an  instrument  has  recently  been  devised 
by  Messrs.  Kent  of  London,  and  is  used  for  measur- 
ing the  discharge  from  the  bacteria  beds  now  in 
course  of  construction  at  Manchester.  It  can  be 
placed  in  the  pick-up  channel  from  the  bed  and  is 
effective  under  three  inches  of  head. 

The  meter  is  shown  in  position  in  Fig.  i.  The 
water  escapes  from  behind  a  dam  through  a  rect- 
angular orifice,  closed  by  a  true-fitting  flap  valve, 
hinged  at  the  top.  The  valve  is  attached  to  a  lever 
which  carries  the  recording  pencil.  As  the  valve 
rises  with  increased  flow,  the  lever  rises  with  it 
and  a  record  of  the  height  during  the  discharge  is 
obtained  on  the  chart  attached  to  the  drum,  which 
revolves  by  clockwork.  The  actual  discharge 
can  be  calculated  from  the  curve  traced  by  the 
pencil. 

A  modification  of  this  instrument  has  also  been 
devised  suitable  for  measuring  the  amount  of  water 
entering  the  bed.  Such  a  measurement  when 
compared  with  the  measurement  of  the  discharge 
affords  a  means  of  more  accurately  determining 
the  volume  of  the  "  drainings  "  from  the  bed. 


8  SEWAGE   WORKS  ANALYSES. 

APPLICATION   OF  ANALYTICAL   METHODS. 

In  order  to  better  understand  the  application  of 
the  methods  of  analysis  given  in  the  following 
pages  it  will  be  convenient  here  to  shortly  indicate 
their  relation  to  the  control  of  the  chief  processes 
of  sewage  treatment  or  purification  as  above 
described,  further  details  being  separately  given  in 
the  case  of  each  process. 

Methods  of  Sampling. — If  accurate  conclusions 
are  to  be  drawn  as  to  the  efficiency  of  any  process, 
it  is  obvious  that  great  care  must  be  taken  to 
obtain  representative  samples. 

Methods  of  Sampling  where  Flow  is  Continuous. — 
In  order  that  the  samples  taken  at  the  inlet  and 
outlet  of  a  precipitation  tank,  for  instance,  should 
be  strictly  comparative,  it  is  evident  that  they 
must  not  be  taken  at  the  same  time,  as  the  effluent 
sample  will  then  represent  the  sewage  of  some 
previous  time,  according  to  the  rate  of  flow 
through  the  tank. 

Approximately  comparative  samples  may  be  ob- 
tained if  the  rate  of  flow  through  the  tank  is  known 
and  the  effluent  sample  taken  at  a  time  when  the 
sewage  in  question  is  passing  away  from  the  tank. 

It  is  better,  however,  to  take  a  sample  of  the 
sewage  and  effluent  at  least  every  hour  during  the 
day.  The  sampling  of  the  tank  effluent  should, 
however,  only  be  begun  after  time  has  been  allowed 
for  the  corresponding  sewage  to  flow  through  the 
tank.  In  the  case  of  the  septic  tank  this  interval 


SEWAGE   WORKS   ANALYSES.  9 

may  amount  to  twenty-four  hours.  In  the  case  of 
chemical  precipitation  tanks  it  may  not  be  more 
than  two  hours.  By  making  up  an  average  sample 
in  equal  proportions  from  these  hourly  samples, 
the  error  due  to  the  mixing  of  the  inflowing  sewage 
with  the  previous  contents  of  the  tank  is  largely 
minimised. 

If  the  average  sample  in  each  case  is  made  up  of 
portions  of  hourly  samples  measured  in  proportion 
to  the  flow  of  sewage  and  effluent  at  the  time,  a 
still  more  representative  sample  is  obtained. 

The  same  principles  of  sampling  apply  to  any 
process  where  the  flow  through  the  installation  is 
continuous  but  variable,  as  for  instance,  septic  tanks 
and  continuous  or  "trickling"  biological  niters. 

Sampling  of  Liquid  Entering  and  Leaving  Contact 
Beds. — In  sampling  the  liquid  entering  and  leaving 
a  contact  bed  it  is  in  general  sufficient  to  take 
two  or  three  samples  and  mix  them,  during  the 
filling  and  emptying  of  the  bed,  as  the  rate  of 
flow  on  and  off  the  bed  should  be  so  regulated 
as  to  be  pretty  constant. 

In  all  cases  where  the  analysis  of  the  sample 
cannot  be  made  at  once,  the  sampling  bottle  should 
be  completely  filled,  and  the  stopper  kept  in  until 
the  sample  is  required  for  analysis.  If  more  than 
a  day  must  pass  before  analysis,  the  samples  should 
be  kept  in  a  cool  place,  preferably  in  an  ice-box. 
It  may  in  some  cases  be  advisable  to  sterilise  the 
samples  by  addition  of  a  little  corrosive  sublimate, 
or  by  making  slightly  acid  with  sulphuric  acid. 


io          SEWAGE   WORKS   ANALYSES. 

Efficiency  of  Catch-pits  and  Screens. — This  is 
determined  by  the  weight  of  material  removed  in 
a  given  time  from  a  given  volume  of  sewage. 

The  detritus  or  garbage  thus  removed  should  be 
weighed  from  time  to  time  after  thorough  draining. 

An  average  sample  collected  from  the  quantity 
thus  weighed  may  be  taken  for  a  proximate 
analysis  (p.  103). 

THE  CONTROL  OF  CHEMICAL  TREATMENT. 

In  order  to  determine  whether  enough  chemical 
has  been  added  to  the  sewage,  a  sample  should 
be  taken  immediately  after  the  addition  of  the 
chemical  and  allowed  to  settle.  No  more  chemical 
should  be  added  than  is  just  sufficient  to  cause 
coagulation  and  pretty  rapid  settlement  with  good 
clarification.  To  add  more  increases  the  volume 
of  sludge  without  increasing  the  purity  of  the 
effluent.  Moreover,  an  excess  of  either  lime, 
alumina,  or  iron,  tends  to  produce  an  effluent 
containing  these  substances  in  solution  from  which 
they  will  afterwards  separate. 

When  lime  and  copperas  are  used  together  it  is 
essential  that  the  lime  be  always  appreciably  in 
excess  of  the  copperas,  in  order  that  precipitation 
may  not  take  place  irregularly  in  the  tanks,  owing 
to  unprecipitated  iron  compounds  coming  into 
contact  with  the  lime.  When,  therefore,  it  is 
necessary  to  increase  the  amount  of  chemicals 
added,  the  lime  should  always  be  increased  first. 

The  presence  of  excess  of  lime  is  indicated  by 


SEWAGE   WORKS   ANALYSES.          n 

the  crimson  colour  produced  on  addition  of 
phenol-phthalein. 

For  the  more  exact  control  of  the  chemicals 
added,  it  may  occasionally  be  necessary,  especially 
with  manufacturing  sewage,  to  carefully  determine 
its  acidity  or  alkalinity  at  different  times  (see  p.  89). 

In  order  to  determine  the  total  amount  of  work 
done  by  the  chemical  treatment,  comparative 
samples  of  the  sewage  and  effluent  should  be 
analysed,  the  samples  being  shaken  before  analysis. 
If  it  is  required  to  know  the  work  done  by  the 
chemicals  alone,  apart  from  the  settlement  in  the 
tanks,  then  the  sewage  samples  should  be  allowed 
to  settle  before  analysis.  As  a  matter  of  fact  it  is 
difficult  to  obtain  a  satisfactory  sample  of  shaken 
sewage,  owing  to  frequent  presence  of  suspended 
matter  in  large  pieces.  The  average  of  a  large 
number  of  analyses  may  be  taken,  however,  to 
furnish  a  sufficiently  accurate  result. 

The  chief  chemical  data  required  to  determine 
the  amount  of  impurity  in  sewage  and  effluent 
are,  the  amount  of  oxygen  absorbed  by  a  known 
quantity  of  the  sample  in  four  hours  and  in  three 
minutes,  the  free  ammonia,  the  albuminoid  am- 
monia and  the  organic  ammonia,  chlorine,  total 
solids  in  solution  and  suspension,  and  sometimes 
the  amount  of  iron. 

The  precise  significance  of  these  determinations 
will  be  indicated  in  the  succeeding  chapters. 

A  fair  measure  of  the  impurities  present  is  given 
by  the  four  hours'  oxygen  absorption  test  and  the 


12         SEWAGE   WORKS  ANALYSES. 

albuminoid  ammonia.  The  purification  effected 
is  generally  calculated  in  percentage,  the  oxygen 
absorption  or  the  albuminoid  ammonia  of  the 
sewage  being  taken  at  100. 

Thus,  if  the  albuminoid  ammonia  of  the  sewage 
was  '75,  and  that  of  the  effluent  "15  grains  per 
gallon,  the  percentage  purification  effected  would 
be 

IPO  X  (75  -  -15)  _  8o 
75 

MEASUREMENT  OF   SLUDGE   PRODUCTION. 

In  all  processes  involving  the  production  of 
sludge  the  quantity  produced  should  be  carefully 
measured,  either  by  collecting  in  storage  tanks  of 
known  dimensions,  or  by  recording  the  quantity 
passed  through  pumps  or  ejectors.  The  percentage 
of  water  contained  in  it  should  also  be  determined 
from  time  to  time.  It  is  obvious  that  the  actual 
quantity  of  solids  removed  can  only  be  calculated 
when  both  the  volume  and  composition  of  the 
sludge  are  known.  Thus,  a  sludge  containing  85  per 
cent,  water  contains  50  per  cent,  more  solid  matter 
than  a  sludge  containing  90  per  cent,  water. 

THE   CONTROL  OF  THE   SEPTIC   TANK. 

The  work  of  the  septic  tank  may  also  be  judged 
by  the  above  tests.  The  determination  of  sus- 
pended matter  in  the  sewage  and  effluent  is  of 
particular  importance  in  this  case,  as  the  amount 
passing  away  tends  to  be  higher  than  when  chemical 


SEWAGE   WORKS   ANALYSES.  13 

treatment  is  made  use  of.  When  the  suspended 
matter  passing  away  becomes  excessive  a  certain 
amount  of  the  sludge  should  be  removed.  It  is 
also  important  that  determinations  of  the  sludge 
present  in  the  tank  should  be  made  from  time 
to  time  (see  p.  109). 

By  determining  the  amount  of  solids  entering 
and  leaving  the  tank  during  a  given  period,  through- 
out which  the  rate  of  flow  through  the  tank  is 
known,  and  by  determining  the  amount  of  sludge 
left  in  the  tank  at  the  end  of  that  period,  some 
idea  may  be  formed  of  the  actual  destruction 
of  sludge  taking  place  in  the  tank. 

Analyses  of  the  gases  evolved  are  of  importance, 
as  the  composition  of  these  varies  with  the  state  of 
the  tank  (see  p.  112),  there  being  more  carbonic  acid 
present  in  the  gases  in  the  early  stages  of  working 
of  a  new  tank  than  after  it  becomes  fully  septic. 

Moreover,  the  composition  of  the  gas  has  been 
found  to  vary  with  the  composition  of  the  sewage, 
there  being  apparently  a  greater  percentage  of 
hydrogen  in  purely  domestic  sewage  than  in  a 
sewage  containing  a  large  proportion  of  manu- 
facturing effluents. 

The  composition  of  the  gas  is  also  found  to 
vary  according  to  the  length  of  time  the  sewage 
remains  in  the  tank,*  and,  altogether,  it  is  prob- 
able that  with  further  research  a  knowledge 
of  the  composition  of  the  gases  evolved  in  the 

*  Report  of  the  Massachusetts  State  Board  of  Health, 
1900,  p.  392. 


I4          SEWAGE  WORKS  ANALYSES. 

septic  tank  will  be  found  of  much  value  in  judging 
of  the  condition  of  the  tank  at  any  time. 

It  is  important,  for  instance,  that  bacterial 
filters  which  have  been  [dealing  with  a  well-septi- 
cised  effluent  should  not  receive  merely  settled 
sewage,  as  not  only  will  they  fail  to  adequately 
purify  it,  but  the  conditions  of  their  activity  tend 
to  be  disturbed.  The  analysis  of  the  septic  tank 
gases  may,  in  such  a  case,  serve  to  show  whether 
septic  changes  are  fully  active  in  the  tank. 

THE  CONTROL  OF   BACTERIAL  FILTERS  AND 
CONTACT  BEDS. 

In  addition  to  the  determinations  of  oxygen 
absorbed,  albuminoid  ammonia,  etc.,  above  men- 
tioned, it  is  important  to  observe  here  the  quantity 
of  nitrite  and  nitrate  present  in  the  filtrate,  as 
these  are  the  final  oxidation  products  of  nitro- 
genous organic  matter.  The  dissolved  oxygen 
present  in  the  filtrate  should  be  determined  from 
time  to  time,  and  also  the  composition  of  the  air 
in  the  interstices  of  the  empty  bed. 

In  the  early  stages  of  working,  the  effluent  from 
bacteria  beds  generally  contains  more  free  and  saline 
ammonia  than  is  present  in  the  tank  effluent  applied, 
owing  to  the  conversion  of  urea  and  albuminoid  com- 
pounds into  ammonium  salts  (see  Chap.  III.).  As 
the  activity  of  the  bed  increases,  the  ammonia  com- 
pounds are  oxidised  to  nitrates,  and  there  will  then 
be  less  free  ammonia  in  the  effluent  from  the  bed 
than  there  is  in  the  tank  effluent  (see  Chap.  IV.). 


SEWAGE   WORKS  ANALYSES.          15 

The  percentage  purification  effected  can  be  calcu- 
lated, as  in  the  case  of  chemical  precipitation,  from  the 
difference  between  the  oxygen  absorption  and  albu- 
minoid ammonia  numbers  before  and  after  filtration. 

If  the  percentage  purification  rapidly  decreases, 
or  if  the  formation  of  nitrates  diminishes  to  a 
marked  extent,  it  is,  in  general,  a  sign  that  the 
filter  is  being  overworked.  The  diminution  of 
nitrates  is  usually  accompanied  by  an  increase  in 
the  production  of  nitrites.  The  presence  of  these 
in  quantity  may  therefore  generally  be  taken  as  a 
sign  that  the  bed  requires  rest. 

On  the  other  hand,  a  knowledge  of  the  dilution 
of  the  sewage  or  tank  effluent  will  indicate  when 
it  is  possible  with  safety  to  increase  the  volume 
put  upon  the  bed. 

It  frequently  happens — during  the  first  flush  of 
a  storm,  for  instance — that  although  the  sewage 
increases  in  volume  it  still  remains  concentrated. 
After  the  first  flush  has  passed,  however,  the 
sewage  becomes  dilute,  and  may  be  dealt  with  by 
the  bacterial  filters  at  a  greater  rate.  The  dilution 
can  generally  be  estimated  by  a  determination  of 
the  chlorine  number  (see  Chap.  VI.). 

Further  details  with  reference  to  the  chemistry  of 
the  changes  taking  place  in  the  septic  tank  and  the 
bacterial  filters  will  be  found  in  the  following  pages. 

METHOD  OF  RECORDING  RESULTS. 

The  quantities  to  be  determined  in  the  analysis 
of  sewage  are  for  the  most  part  so  small  that  they 


16          SEWAGE  WORKS   ANALYSES. 

cannot  conveniently  be  expressed  in  percentages. 
The  simplest  method  is  undoubtedly  to  record 
results  in  parts  per  100,000.  To  be  consistent, 
the  sewage  should  then  itself  be  measured  in  cubic 
metres,  when  the  quantity  of  impurity  present 
would  bear  a  simple  relation  to  the  total  volume 
of  sewage. 

In  England,  however,  liquids  are  still  measured 
in  gallons,  and  therefore  in  the  following  pages 
the  results  are  determined  in  grains  per  gallon,  so 
that  the  amount  of  impurity,  etc.,  in  the  total 
volume  of  sewage  can  easily  be  calculated. 

The  results  recorded  in  grains  per  gallon  can 
readily  be  converted  into  parts  per  100,000,  if  it  is 
remembered  that  one  grain  per  gallon  is  one  part 
in  70,000.  To  convert  grains  per  gallon  into  parts 
per  100,000  the  results  must  be  divided  by  7. 
On  the  other  hand,  grains  per  gallon  will  be  '7  of 
parts  per  100,000.  A  table  will  be  found  on  page 
128  in  which  the  corresponding  values  of  these  two 
methods  are  given  over  a  convenient  range  of 
numbers. 

In  determining  the  nitrogen  in  the  various  forms 
in  which  it  occurs  in  sewage  and  sewage  effluents, 
it  is  important  that  the  results  should  all  be  ex- 
pressed in  similar  terms,  in  order  to  be  comparable. 
As  the  nitrogen,  whether  present  as  ammonia, 
albuminoid  compounds  or  nitrates,  is  eventually 
determined  as  ammonia,  it  has  been  found  con- 
venient to  record  it  in  terms  of  the  ammonia 
produced  in  each  case. 


.      SEWAGE  WORKS  ANALYSES.          17 

The  Royal  Commission  on  Sewage  Disposal  ask 
for  the  results  to  be  expressed  in  terms  of  nitrogen, 
i.e.,  ammoniacal  nitrogen,  albuminoid  nitrogen, 
nitric  nitrogen,  etc.  In  this  case  the  ammonia 
produced  in  the  analytical  process  must  be  multi- 
plied by  "82  (  i.e.  ^=-  =  -z  )  in  order  to  give 

N          .N  jri3          17  / 

the  value  as  nitrogen. 

Calculation  may  of  course  be  saved  if  the  strength 
of  standard  solutions  and  the  quantity  of  the  sample 
taken  for  analysis  are  so  arranged  as  to  give  the 
result  required  at  once.  In  the  following  descrip- 
tions alternative  quantities  are  given  where  it 
appears  necessary. 

It  may  be  here  remarked  that  it  is  possible  to 
attempt  too  great  refinement  in  the  methods  used 
for  the  analysis  of  sewage,  inasmuch  as  except 
when  sterile  it  is  constantly  subject  to  progressive 
changes  in  composition.  Analyses  which  record  a 
fourth  or  even  third  place  of  decimals  give  really 
a  fictitious  appearance  of  accuracy. 

DEGREE  OF  PURITY  NECESSARY  IN  AN  EFFLUENT. 

Considerable  difference  of  opinion  exists  as  to 
the  degree  of  purification  necessary  to  be  obtained 
in  an  effluent,  and  various  standards  of  purity  or 
limits  of  impurity  of  a  somewhat  arbitrary  character 
have  been  provisionally  adopted  by  various  con- 
servancy boards. 

For  example,  the  Mersey  and  Irwell  Joint  Com- 
mittee class  as  good  any  effluent  which  absorbs 

s.w.  c 


i8          SEWAGE  WORKS  ANALYSES. 

less  than  one  grain  per  gallon  of  oxygen  from 
permanganate  in  four  hours,  and  which  evolves 
less  than  one  grain  per  gallon  albuminoid  ammonia. 

In  the  reports  of  the  chief  inspector  to  the 
Ribble  Joint  Committee  sewage  effluents  areclassed 
as  good  if  the  albuminoid  ammonia  liberated  is 
below  *i  part  per  100,000,  suspended  matter 
absent,  and  the  presence  of  nitrates  confirmed.* 

The  Derbyshire  County  Council  define  a  good 
effluent  as  one  which  contains  less  than  *i  part 
per  100,000  of  albuminoid  ammonia,  and  which  con- 
tains more  than  '5  parts  per  100,000  of  nitrogen 
as  nitrates.  It  should  also  be  so  thoroughly 
oxidised  that  it  does  not  absorb  more  oxygen  after 
incubation  for  one  week  than  it  does  at  the  time 
of  collection. 

While  such  "limits  "  have  their  undoubted  uses 
in  stimulating  authorities  to  efficiently  purify  their 
sewage,  yet  it  is  obvious  that  they  are  of  an 
empirical  nature. 

When,  for  example,  an  effluent  flows  into  a 
tidal  river  or  into  the  sea,  or  where  the  volume  of 
effluent  is  very  small  in  comparison  with  the  volume 
of  river  water,  a  degree  of  purification  represented 
by  the  *i  grain  per  gallon  albuminoid  ammonia  of 
the  Mersey  and  Irwell  Joint  Committee  would  prob- 
ably be  altogether  unnecessary,  as  the  river  would 
contain  enough  oxygen  to  oxidise  the  residual 
impurity.  On  the  other  hand,  such  an  effluent 

*  W.  Naylor,  "  Rivers  Pollution  Standards,"  "  Journal 
of  the  Sanitary  Institute,"  vol.  xix.,  part,  i.,  p.  24. 


SEWAGE  WORKS  ANALYSES.          19 

might  be  quite  insufficiently  purified  to  enter  a 
stream  which  is  afterwards  used  for  a  water  supply. 

Cases  of  this  sort  are  illustrated  by  the  Thames 
above  the  intakes  of  the  London  water  companies, 
or  by  the  Dee  above  the  Chester  water  supply. 
The  Massachusetts  experiments  on  sewage  puri- 
fication were  undertaken  in  order  to  diminish  the 
occurrence  of  typhoid  in  towns  deriving  their  water 
supply  from  sewage-polluted  rivers.  In  this  case 
a  high  degree  of  purification  had  to  be  aimed  at, 
and  the  experimental  filters  were  constructed  for 
the  most  part  of  sand. 

Again,  the  effluent  may  contain  organic  matter 
in  excess  of  the  limits  allowed  by  any  of  the  above- 
mentioned  authorities,  and  yet  maintain  in  solution 
an  amount  of  oxygen  or  of  nitrates  more  than 
sufficient  to  oxidise  this  residual  impurity  after 
a  short  lapse  of  time.  Moreover,  the  oxygen 
absorbed  from  permanganate  by  the  effluent  maybe 
due  to  oxidisable  substances  other  than  putrefac- 
tive organic  matter,  resulting  from  manufacturing 
processes  which  may  be  incapable  of  causing  a 
nuisance  or  of  robbing  the  stream  of  oxygen. 

Apart  from  such  provisional  limits  of  impurity, 
it  is  evident  that  the  character  of  the  effluent  as  a 
whole  must  be  considered  together  with  the  stream 
into  which  it  flows. 

This  is  indeed  recognised  by  the  authorities 
themselves,  who  in  taking  action  have  regard,  in 
general,  to  all  the  circumstances  of  the  case. 

Broadly  speaking,  it  may  be  taken  that  no  serious 

c  2 


20          SEWAGE   WORKS  ANALYSES 

pollution  will  occur  in  practice  if  the  effluent  is  so 
far  purified  that  it  will  always  leave  a  fair  surplus 
of  dissolved  oxygen  in  the  stream  into  which  it 
flows.  This  may  be  roughly  tested  by  mixing  the 
effluent  with  an  equal  volume  of  the  stream  and 
incubating  the  mixture  for  two  days,  during  which 
time  no  putrefaction  should  occur. 

It  may  sometimes  happen  that  the  effluent  pro- 
duced is  better  than  the  stream  which  receives  it. 
For  example,  the  Manchester  Ship  Canal  in  the 
summer  months  is  itself  in  a  state  of  putrefaction 
before  the  Manchester  effluent  enters  it. 

In  such  a  case  the  effluent  must  be  judged  by 
other  tests  than  the  one  just  mentioned.  For  such 
tests  reference  may  be  made  to  Chap.  V.,  p.  82. 

Briefly,  the  method  consists  in  presenting  a 
known  amount  of  dissolved  oxygen  to  the  effluent, 
by  mixing  it  with  a  given  volume  of  aerated  water 
and  noting  the  diminution  of  dissolved  oxygen 
which  occurs  after  two  days'  incubation. 

For  further  information  as  to  the  principles  of 
sewage  purification  and  the  methods  used  in  various 
cases  the  following  works  may  be  consulted  : — 

DIBDIN  :  "  Purification  of  Sewage  and  Water." 

RIDEAL  :  "  Sewage  and  Sewage  Purification  " 
(Sanitary  Publishing  Co.). 

LAFAR:  "  Technical  Mycology  "  (Griffin  &  Co.). 

"  Reports  of  the  Massachusetts  State  Board  of 
Health  "  (P.  S.  King  &  Son,  Westminster). 

"  Manchester  Sewage  Reports  "  (P.  S.  King  & 
Son,  Westminster). 


SEWAGE   WORKS   ANALYSES.          21 


CHAPTER  II. 

THE     DETERMINATION     OF     ABSORBED 
OXYGEN. 

THEORY  OF  THE   PROCESS. 

WHEN  an  organic  substance — e.g.,  coal — is 
burnt  it  combines  with  oxygen  and  is  said  to 
be  oxidised. 

The  amount  of  oxygen  combined  in  this  way  is 
evidently  a  measure  of  the  quantity  of  coal  or 
other  combustible  or  oxidisable  substance  burnt. 

The  organic  matter  in  sewage  could  be  obtained 
in  the  dry  state  by  evaporation,  and  in  like  manner 
its  amount  could  be  estimated  by  determining  the 
amount  of  oxygen  required  to  burn  it. 

It  is  more  convenient,  however,  to  oxidise  the 
organic  matter  while  in  solution,  by  addition  of 
some  compound  which  will  readily  yield  up  its 
oxygen  to  the  oxidisable  substances  present. 

Such  a  compound  is  potassium  permanganate, 
and  the  oxidation  thus  carried  out  is  termed  "  moist 
combustion." 

The  amount  of  "  oxygen  absorbed  "  from  potas- 
sium permanganate  in  acidified  solution  is  taken 
as  a  measure  of  the  organic  or  other  oxidisable 
matter  present. 


22          SEWAGE   WORKS  ANALYSES. 

The  action  of  the  permanganate  may  be  better 
understood  from  the  following  equation  : — 

2KMnO4  +  3H2SO4  (+  oxidisable  matter)  = 
K2  SO4  +  2MnSO4  +  3H2O  +  50  (combined  with 
oxidisable  matter).* 

This  indicates  that  316  parts  of  pure  potassium 
permanganate  will  yield  80  parts  of  oxygen  to 
oxidisable  matter,  in  presence  of  sulphuric  acid, 
or  "395  grm.  KMnO4  will  yield  'ioo  grm.  oxygen. 
If  '395  grm«  KMnO4  is  dissolved  in  i  litre 
(1000  c.c.)  of  water,  each  c.c.  of  the  solution  will 
yield  T\j  mgrm.  oxygen. 

In  order  to  determine  exactly  the  amount  of 
oxygen  absorbed  from  the  permanganate  it  is 
necessary  to  add  excess  of  this  reagent  to  the 
liquid  to  be  tested,  and  after  a  given  time  to 
determine  the  oxygen  still  unabsorbed. 

This  can  be  most  accurately  accomplished  by 
addition  of  potassium  iodide,  when  iodine  is 
liberated  in  amount  equivalent  to  the  unabsorbed 
oxygen  thus : — 

5O  (as  permanganate)  +  loKI  -f  5H2SO4  = 
5K2S04  +  5l2  + 5H20. 

This  iodine  and  consequently  the  unabsorbed 
oxygen  can  then  be  determined  by  addition  of 

*  Potassium  permanganate  may  be  looked  upon  as  a 
compound  of  the  basic  oxide  K2O  and  the  acid  oxide  Mn2O7 
(thus  2KMnO4  =  K2OMn2O7).  In  the  above  equation 
the  Mn2O7  is  reduced  to  the  basic  manganous  oxide  MnO 
with  liberation  of  5  atoms  of  O.  The  sulphuric  acid  serves 
to  neutralise  the  KaO  and  MnO,  forming  potassium  and 
manganous  sulphates. 


SEWAGE   WORKS  ANALYSES.          23 

sodium  thiosulphate  solution  of  known  strength, 
when  sodium  tetra  thionate  and  sodium  iodide  are 
formed,  thus : — 

5X2  +  ioNa2S2O3  =  5Na2S4O6  +  loNal. 
The  exact  point  at  which  the  iodine  is  all  com- 
bined may  be  determined  by  the  addition  of  a  few 
drops  of  starch  solution,  which  gives  a  deep  blue 
colour  with  free  iodine.  When  all  the  iodine  is 
combined  the  blue  colour  is  at  once  discharged. 
The  method  is  carried  out  in  detail  in  practically 
the  same  manner  in  the  laboratories  of  the  Mersey 
and  Irwell  Joint  Committee  and  of  the  Manchester 
Corporation. 

SOLUTIONS   REQUIRED. 

For  the  determination  of  oxygen  absorption  the 
following  solutions  are  therefore  required : — 

Potassium  Permanganate. — '395  grm.  of  the  pure 
crystallised  salt  is  dissolved  in  i  litre  of  water 
which  has  been  very  faintly  tinged  with  perman- 
ganate solution  in  order  to  oxidise  any  impurities 
in  the  water.  It  is  often  convenient  to  dissolve 
three  times  the  above  quantity  and  dilute  to  3  litres 
in  a  large  Winchester  bottle;  but  it  is  not  advis- 
able to  make  up  much  more  than  a  day's  supply 
at  once,  as  the  solution  is  liable  to  be  reduced  by 
floating  dust,  etc. 

Sulphuric  Acid. — One  part  of  the  pure  acid  is 
carefully  added  to  3  parts  of  water  contained  in  a 
large  thin  flask,  which  should  be  gently  rotated  as 
the  acid  is  added,  in  order  to  prevent  too  great 


24          SEWAGE   WORKS   ANALYSES. 

heating.  The  mixture  must  be  cooled  before  use, 
or  before  transferring  to  a  bottle.  As  in  the  case 
of  the  water  used  for  dissolving  the  potassium 
permanganate,  it  is  advisable  to  add  to  the  cold 
diluted  acid  a  few  drops  of  potassium  permanga- 
nate solution,  until  a  faint  but  permanent  pink 
tinge  is  produced. 

Potassium  Iodide. — Ten  grms.  of  potassium 
iodide  are  dissolved  in  100  c.c.  of  water.  It  is 
not  advisable  to  make  up  a  larger  quantity  of 
potassium  iodide  solution  than  is  needed  for  im- 
mediate requirements,  as  it  suffers  decomposition 
when  exposed  to  air  and  light. 

Starch  Solution. — Two  grms.  of  starch  are  rubbed 
down  with  a  little  water  to  a  smooth  cream;  this 
is  poured  carefully  into  a  litre  of  already-boiling 
water  in  a  large  flask  (if  added  too  quickly,  the 
water  may  boil  over).  The  solution  is  boiled  for 
a  few  minutes  after  the  addition  of  the  starch,  till 
quite  clear,  and  then  allowed  to  cool  under  the 
water  -  tap.  After  settling,  the  clear  liquid  is 
decanted  for  use. 

Sodium  Thiosulphate. — This  may  conveniently  be 
made  of  such  a  strength  that  i  c.c.  =  2  c.c.  of  the 
permanganate  solution.  For  this  purpose,  about 
7  grms.  pure  crystallised  sodium  thiosulphate 
(" hyposulphite  of  soda")  are  dissolved  in  i  litre  of 
water  (or  three  times  this  quantity  may  be  taken). 
A  blank  test  is  then  made  with  a  mixture  of  70  c.c. 
of  distilled  water,  10  c.c.  of  the  sulphuric  acid, 
and  50  c.c.  of  the  permanganate  solution.  A  few 


SEWAGE   WORKS   ANALYSES.         25 

drops  of  the  iodide  solution  are  added  to  this  till 
the  clear  yellowish-brown  colour  of  the  iodine  is 
obtained.  The  thiosulphate  solution  is  now  run 
in  from  a  burette  till  the  iodine  colour  is  reduced 
to  a  pale  yellow,  a  few  drops  of  starch  solution 
are  added  and  a  small  additional  quantity  of 
thiosulphate  run  in  till  the  blue  colour  just 
disappears. 

If  the  thiosulphate  is  present  in  exactly  the 
right  proportion,  25  c.c.  of  the  solution  should  be 
equivalent  to  the  50  c.c.  of  permanganate.  If  the 
solution  is  strong,  as  will  be  probably  the  case, 
say  24  c.c.  thiosulphate  =  50  c.c.  permanganate, 
then  for  every  24  c.c.  remaining  of  the  thiosul- 
phate solution,  i  c.c.  of  water  must  be  added, 

1000  -  24  ,      3000  -  24 

viz.,  — — ^  =  32-3  c.c.  (or  ^=124  c.c., 

if  3  litres  have  been  made  up). 

With  a  little  practice  a  solution  of  thiosulphate 
may  be  in  this  manner  easily  adjusted  so  that 
25  c.c.  =  50  c.c.  permanganate.  The  solution  does 
not  keep  long  unchanged,  and  should  be  read- 
justed every  day  at  least,  but  the  slight  trouble 
thus  involved  saves  a  great  deal  of  calculation 
where  many  analyses  have  to  be  made. 

The  method  above  described  for  adjusting  the 
thiosulphate  solution  closely  resembles  the  method 
used  for  determining  oxygen  absorption,  the  70  c.c. 
distilled  water  being  replaced  by  the  sample  to  be 
tested. 


26          SEWAGE   WORKS   ANALYSES. 


METHOD   OF   CARRYING   OUT   DETERMINATIONS. 

Measurement  of  Solutions. — In  measuring  quanti- 
ties of  sewage  or  effluent  it  is  inadvisable  to  use 
a  pipette,  owing  to  risk  of  sucking  up  noxious 
emanations,  or  even  some  of  the  liquid  itself  into 
the  mouth.  A  100  c.c.  graduated  measuring 
cylinder  will  be  found  convenient,  the  liquid  being 
always  measured  from  the  tangent  to  the  meniscus. 

The  various  reagents  can  be  added  most  expedi- 
tiously  from  burettes,  these  being  slightly  widened 
at  the  top  to  admit  of  rapid  filling.  The  burettes 
should  always  be  kept  corked  when  not  in  use,  to 
prevent  entrance  of  dust,  etc. 

Where  only  a  few  drops  of  a  reagent  have  to  be 
added,  a  dropping  bottle  may  be  used.  This  is 
made  by  simply  cutting  a  notch  in  the  side  of  the 
cork  which  fits  the  neck  of  the  bottle  containing 
the  reagent.  On  inverting  and  shaking  the  bottle, 
the  liquid  is  delivered  in  drops. 

To  carry  out  the  determination,  70  c.c.  of  the 
sample  to  be  analysed  are  taken  (more  if  it  con- 
tains very  little  oxidisable  matter,  less  if  it  contains 
very  much),  10  c.c.  of  sulphuric  acid  are  added,  and 
then  50  c.c.  of  the  permanganate  solution.  The 
mixture  is  allowed  to  stand  four  hours  in  a  stoppered 
bottle.  For  this  purpose,  the  glass  jars  in  which 
stick  potash  is  sold  may  be  conveniently  used. 
While  standing,  the  bottle  should  be  kept  corked. 

It  is  important  that  excess  of  permanganate 
should  always  be  present  during  the  four  hours. 


SEWAGE  WORKS  ANALYSES.          27 

If  it  becomes  markedly  decolourised  before  the 
four  hours  have  expired,  a  second,  and,  if  neces- 
sary, a  third  quantity  of  acid  and  permanganate 
solution  is  added.  It  frequently  also  happens,  if 
suspended  oxidisable  matter  is  present,  that  the 
solution  begins  to  be  decolourised  at  the  bottom. 
In  this  case  it  should  be  shaken  from  time  to  time 
to  thoroughly  oxidise  the  suspended  matter. 

At  the  end  of  four  hours  a  few  drops  of  the 
potassium  iodide  solution  are  added  till  the  clear 
orange  colour  of  the  iodine  is  obtained.  The 
sample  is  then  titrated  with  thiosulphate  and 
starch  solution  as  described  above. 

The  number  of  c.c.  of  thiosulphate  added  is 
carefully  noted. 

The  oxygen  absorption  is  calculated  as  follows : — 

When  10  c.c.  KMnO^  =  i  mgrm.  O, 

I  c.c.  Na2S2O3  =  2  c.c.  KMnO*. 
If  a  =  c.c.  of  permanganate  used, 

b  —  c.c.  of  thiosulphate  used, 
a  —  26  =  grains    of    oxygen    absorbed    per 
10  gallon  of  sample. 

For  example,  if  70  c.c.  of  the  sample  have  been 
taken,  50  c.c.  of  permanganate  added,  and  22  c.c. 
of  thiosulphate  are  needed  for  the  final  titration, 
then  one  gallon  of  the  sample  will  absorb — 

5_Zj: 1  —  «5  grains  per  gallon  oxygen. 

In  some  cases  (e.g.,  where  only  a  few  samples 
have  to  be  examined)  it  may  not  be  convenient 
to  adjust  the  thiosulphate  solution  to  correspond 


28          SEWAGE   WORKS   ANALYSES. 

exactly  with  the  permanganate  as  above  described, 
then  the  oxygen  absorbed  by  each  sample  must  be 
calculated  as  follows,  from  a  blank  experiment 
made  every  day  : — 

Example  from  Mr.  Scudder's  Note-book : — 

Test.  Blank. 

10  c.c.  sulphuric  acid.          10  c.c.  sulphuric  acid. 
50  c.c.  potassium  per-        50  c.c.  potassium  per- 
manganate, manganate. 
70  c.c.  sewage  effluent.        70  c.c.  distilled  water. 

Required    24*0    c.c.  Required    27*7    c.c. 

NasSsOs  solution.  Na2S2O3solution. 

5°  c'c-    KMn04  solution 
27*7  c.c.    Na2S2O3 
Multiply  the  thiosulphate  figure  obtained  in  the 
test  by  the   factor,  and   the   amount  of  unused 
permanganate  will  be  obtained. 

24*0  x  1*8  =  43*2  c.c.  permanganate  solution. 

50  c.c.  KMnO4  solution  —  43*2  c.c.  =  6*8  c.c. 
KMnO4  used. 

i  c.c.  KMnOi  =  o'l  mgrm.  oxygen. 

6*8  x  0*1  =  0*68  mgrm.  oxygen  absorbed  by 
70  c.c.  sewage  effluent. 

=  0'68  grains  oxygen  absorbed  per  gallon,  four 
hours'  test. 

In  doing  a  large  number  of  determinations,  it 
will  be  found  most  convenient  and  satisfactory  to 
measure  out  the  acid  and  permanganate  first  into 
the  bottles,  and  then  add  a  sample  to  each  bottle 
in  turn. 

The  iodine  and  thiosulphate  must  be  added  to 


SEWAGE   WORKS  ANALYSES. 


the  first  sample  of  the  series  four  hours  after  it  has 
been  mixed  with  the  acid  and  permanganate. 

The  time  of  titration  may  be  rather  more  than 
that  required  to  add  the  sample  to  the  perman- 
ganate in  the  first  instance.  The  action  of  the 
permanganate  can,  however,  be  stopped  at  any 
point  by  addition  of  potassium  iodide  ;  but  if  this 
is  allowed  to  remain  long  before  addition  of  thio- 
sulphate,  error  is  likely  to  arise,  owing  to  a  further 
liberation  of  iodine  from  the  iodide  by  the  action 
of  sulphuric  acid  in  the  presence  of  light. 

The  following  are  some  typical  examples  of  the 
results  of  the  application  of  this  test  to  sewage  and 
effluents  of  various  descriptions  — 


Description  of  Sample. 

Oxygen  absorbed, 
4  hours'  test. 

Grains  per 
Gallon. 

Parts  per 
100,000. 

MANCHESTER  SEWAGE  (containing  much 
manufacturing  refuse)  — 
Sewage     (sample    shaken    before 
analysis)      ...         ...        ...         ... 

8'57 
5'84 

4-88 
5-88 

1-87 
•58 
3-60 

2'00 
'55 

I2'24 

8-34 

6-97 
8-40 

2'67 
•83 

5'i4 
2-86 
•80 

Sewage     (sample     settled    before 

Effluent  from    chemical  precipita- 
tion (lime  and  copperas) 
Effluent  from  open  septic  tank     ... 
Effluent  from  open  septic  tank  after 
i  contact  on  bacteria  beds 
Effluent  from  open  septic  tank  after 
2  contacts  on  bacteria  beds 
OLDHAM  SEWAGE   (mainly  domestic)  — 
Sewage           
Effluent  after  settlement  in  tanks... 
Filtrate  from  single  contact 

30          SEWAGE  WORKS  ANALYSES. 

Substances  other  than  Domestic  Sewage  indicated  by 
Four  Hours'  Test. — Although  the  amount  of  oxygen 
absorbed  is  a  good  measure  of  the  impurities 
present  in  domestic  sewage,  yet  in  cases  where 
manufacturing  refuse  is  present,  the  permanganate 
is  reduced  by  substances  other  than  sewage.  In 
some  cases  these  may  be  equally  capable  of  putre- 
faction, and  consequently  of  producing  a  nuisance. 
The  following  are  examples  of  such  substances : — 

Brewery  waste,  yeast,  etc. 

Size  manufacturers'  refuse. 

Abattoir  refuse. 

Paper  waste. 

Distillery  waste. 

Tannery  and  fellmongering  refuse. 

Wool-scouring  refuse. 

Other   substances,   however,  may    be    present 
which    are    not    putrefactive,  but  which   absorb 
oxygen.     Such  are  the  following  : — 
Various  coal-tar  products,  e.g., 

Phenol. 

Naphthylamine. 

Naphthol,  etc. 

Naphthalene  sulphonic  acids. 

Pyridine  bases. 
Dyes,  e.g.— 

Indigo. 

Logwood,  etc. 
Inorganic  salts,  e.g. — 

Thiocyanates. 

Sulphites. 


SEWAGE   WORKS   ANALYSES.  31 

Iron-pickle,  etc. 
Nitrites. 

Three  Mimites'  Oxygen  A  bsorption  Test. — The  deter- 
mination of  the  oxygen  absorbed  by  permanganate 
in  three  minutes,  i.e.,  practically  instantaneously, 
gives  a  means  of  differentiating  between  one  class 
of  oxidisable  substances  and  another,  and  in  con- 
junction with  the  incubator  affords  an  excellent 
method  of  determining  the  amount  of  putrefaction 
which  is  capable  of  taking  place  in  a  sample  of 
sewage  or  effluent. 

For  strictly  comparative  tests  the  following 
method,  closely  resembling  the  process  for  deter- 
mining the  oxygen  absorbed  in  four  hours,  is 
recommended : — 

Seventy  c.c.  of  the  sample  are  taken  (more  if  it 
contains  very  little  oxidisable  matter,  less  if  it 
contains  very  much),  10  c.c.  of  sulphuric  acid  are 
added,  and  then  50  c.c.  of  permanganate  as  before ; 
but  the  action  of  the  permanganate  is  stopped  by 
the  addition  of  potassium  iodide  at  the  end  of 
three  minutes,  and  the  sample  titrated  as  before 
with  sodium  thiosulphate  and  starch. 

When  a  large  number  of  samples  has  to  be 
examined  the  following  method  will  be  found 
convenient : — 

Add  the  acid  and  permanganate  solution  to  all 
the  bottles  necessary,  including  (if  the  thiosulphate 
is  not  exactly  adjusted)  the  blank  test.  Then 
start  at  one  end  of  the  row  and  each  half-minute 
add  70  c.c.  of  the  effluent  to  be  tested. 


32         SEWAGE  WORKS   ANALYSES. 

When  the  seventh  bottle  is  reached  the  first 
bottle  will  have  stood  three  minutes,  and  is  stopped 
by  adding  an  excess  of  potassium  iodide  solution. 
When  the  eighth  bottle  is  reached  the  second  will 
be  stopped,  and  so  on,  until  the  series  is  complete. 
Each  one  is  then  titrated  in  succession  with  thio- 
sulphate,  until  the  blank  is  reached  from  which  the 
factor  is  obtained,  as  in  the  four  hours'  test. 

The  proportion  of  permanganate  to  sample 
should  be  such  that  at  least  30  per  cent,  of  the 
permanganate  solution  remains  unchanged. 

The  results  are  calculated  as  in  the  case  of  the 
four  hours'  test. 

Substances  other  than  Domestic  Sewage  which 
affect  the  Three  Minutes'  Test.  —  The  following 
substances  which  may  occur  in  sewage  containing 
manufacturing  waste  are  completely  oxidised  by 
acid  permanganate  at  once  : — 

Iron  pickle. 

Sulphites. 

Sulphocyanates. 

Sulphides. 

Nitrites. 

Phenol. 

Naphthylamine. 

Naphthalene  sulphonic  acids. 

Indigo. 

The  other  substances  specially  mentioned  when 
describing  the  four  hours'  test  will,  of  course,  also 
affect  the  three  minutes'  test. 

Use    of  Three   Minutes'    Test    by    Workmen. — 


SEWAGE   WORKS   ANALYSES.         33 

Experience  in  any  particular  sewage  will  show 
that  a  fairly  constant  average  relation  exists 
between  the  three  minutes'  oxygen  absorption 
and  the  four  hours'  oxygen  absorption,  albuminoid 
ammonia,  etc.,  tests. 

Thus,  in  the  case  of  many  domestic  sewages  a 
three  minutes'  oxygen  absorption  of  "25  grain  per 
gallon  indicates  satisfactory  purification. 

With  Manchester  sewage,  which  contains  much 
oxidisable  manufacturing  refuse,  '5  grain  per 
gallon  may  be  accepted. 

The  three  minutes'  absorption  test  may  there- 
fore be  applied  in  a  modified  form  as  a  rough-and- 
ready  test  for  the  control  of  bacteria  beds,  when 
the  number  of  samples  would  render  continual 
complete  analyses  impracticable. 

In  order  to  place  the  test  in  the  hands  of  an 
intelligent  workman  the  following  modification 
may  be  adopted : — 

'395  grm-  of  permanganate  is  taken  and  made 
up  in  the  laboratory  to  one  litre  with  200  c.c.  sul- 
phuric acid  (i  acid,  3H2O),  and  800  c.c.  water.  A 
strong  glass  cylinder  (e.g.,  a  potash  jar)  is  graduated 
with  a  file  in  two  places,  the  lower  mark  indicating 
140  c.c.,  and  the  interval  between  the  two  marks 
corresponding  to  20  c.c. 

It  is  then  easy  for  the  workman  to  measure 
140  c.c.  of  the  sample  to  be  tested  and  to  add 
20  c.c.  of  the  acid  permanganate. 

If  the  colour  completely  disappears  in  three 
minutes,  the  sample  is  inadequately  purified. 

S.W.  n 


34          SEWAGE   WORKS   ANALYSES. 

A  little  practice  in  noting  the  rapidity  of  the  de- 
colourisation  will  soon  enable  a  workman  to  judge 
of  the  character  of  the  purification  he  has  obtained. 

It  is  important  that  the  permanganate  solution 
should  be  freshly  made  up  every  few  days. 

THE   INCUBATOR  TEST. 

When  a  sample  of  sewage  or  effluent  undergoes 
putrefaction,  products  such  as  sulphuretted  hy- 
drogen are  formed,  which  are  rapidly  oxidised  by 
permanganate;  i.e.,  the  three  minutes'  oxygen 
absorption  of  a  sample  after  putrefaction  is 
greater  than  when  the  sample  is  fresh. 

Upon  this  fact  Mr.  F.  Scudder,  chemist  to  the 
Mersey  and  Irwell  Joint  Committee,  has  based  a 
convenient  method  for  ascertaining  the  tendency 
of  a  sample  to  undergo  putrefaction. 

A  determination  of  the  oxygen  absorbed  in  three 
minutes  by  the  sample  is  made.  A  small  bottle  is 
then  completely  filled  with  the  sample,  the  stopper 
is  inserted,  and  the  full  bottle  placed  in  an  incu- 
bator and  maintained  at  a  constant  temperature 
corresponding  to  a  warm  summer  day  for  five  or 
six  days,  and  the  three  minutes'  oxygen  absorption 
again  determined. 

In  the  Mersey  and  Irwell  Joint  Committee's  labo- 
ratory 75°  F.  (24°  C.)  is  the  temperature  chosen, 
and  the  sample  is  kept  in  the  incubator  five  days. 

In  the  laboratory  of  the  Manchester  Corporation 
Sewage  Works  80?  F.  (26°  C.)  is  taken,  and  the 
sample  incubated  for  six  or  seven  days. 


FIG.  2.— THE    HEARSON    INCUBATOR. 


[To  face  page  35. 


SEWAGE   WORKS  ANALYSES.         35 

The  time  and  temperature  chosen  are,  to  some 
extent,  a  question  of  convenience.  It  is  preferable, 
for  example,  that  samples  should  not  have  to  be 
taken  from  the  incubator  on  Saturday  or  Sunday. 

The  most  convenient  and  trustworthy  form 
of  incubator  is  the  Hearson  incubator  (see  Fig.  2). 
It  is  essentially  a  water-jacketed  chamber,  heated 
by  a  regulated  gas  supply.  The  temperature  is 
controlled  by  means  of  the  expansion  and  con- 
traction of  a  capsule  containing  a  liquid  of  suitable 
boiling  point.  As  the  temperature  rises,  the 
capsule  expands,  lifting  a  weighted  rod,  which 
cuts  off  the  gas  supply.  Full  directions  for  setting 
up  and  adjusting  the  incubator  are  given  with  the 
apparatus.  A  4-02.  or  8-oz.  bottle  is  the  size 
suitable  for  ordinary  incubator  tests. 

A  simple  incubator  can  be  made  by  fitting  up  an 
ordinary  water-jacketed  air-bath  with  a  Page  or 
Reichardt  gas  regulator. 

The  difference  between  the  three  minutes'  oxygen 
absorption  before  and  after  incubation  is  a  measure 
of  the  change  which  has  taken  place  in  the  sample. 
If  the  oxygen  absorption  increases,  the  production 
of  easily  oxidisable  substances  such  as  sulphides  is 
indicated,  and  the  amount  of  increase  is  therefore 
a  measure  of  the  putrefaction  which  has  taken 
place  ;  or  in  other  words,  the  difference  represents 
the  tendency  of  the  sample  to  cause  a  nuisance 
when  exposed  to  conditions  favourable  to  putre- 
faction. An  exception  may  occur  in  the  case  of 
effluents  containing  nitrates.  In  this  case  the 

D  2 


36          SEWAGE   WORKS   ANALYSES. 

nitrates  may  be  reduced  by  the  organic  matters 
present,  with  formation  of  nitrites.  These  absorb 
oxygen  from  permanganate  immediately,  and  it 
may  happen  in  this  way  that  the  three  minutes' 
test  is  greater  after  incubation  than  before,  but  no 
putrefaction  has  taken  place.  In  such  cases  nitrites 
should  be  looked  for  and  determined  if  found,  by 
the  Griess-Ilosvay  test  described  later  (p.  64). 

If  nitrites  are  found  to  be  present,  they  may  be 
destroyed  by  adding  a  little  urea  to  the  acid 
solution,  when  the  following  reaction  occurs  :  — 


The  titration  with  permanganate,  etc.,  may 
then  be  repeated. 

In  the  case  of  a  sample  which  contains  dissolved 
oxygen  or  nitrates,  the  three  minutes'  test  will  in 
general  be  less  after  incubation  than  before,  even 
if  nitrites  are  present.  Such  decrease,  therefore, 
indicates  efficient  purification. 

It  may  sometimes  happen  in  the  case  of  sewage 
containing  manufacturing  refuse  that  substances 
are  present  which  either  retard  or  even  entirely 
inhibit  putrefaction.  Or  so  much  lime  is  some- 
times added  in  chemical  treatment  that  the 
resultant  effluent  is  sterile.  In  such  cases  little 
if  any  change  will  be  indicated  by  this  test. 

To  properly  judge  of  the  character  of  such  an 
effluent,  it  should  be  mixed  with  an  equal  volume 
of  the  stream  into  which  it  is  destined  to  flow, 
and  the  mixture  re-incubated.  The  effect  of  the 
sterilising  substance  is  thus  diminished  or  entirely 


SEWAGE   WORKS   ANALYSES. 


37 


prevented,  and  putrefaction  will  take  place  if  the 
sample  is  not  properly  purified. 

Of  considerable  interest  is  the  determination  of 
dissolved  oxygen  and  nitrates  in  a  sample  after 
incubation.  This  will  be  further  referred  to  in 
Chapters  IV.  and  V. 

The  following  examples  will  illustrate  some  of 
the  points  referred  to  in  connection  with  the 
incubator  test. 


3  Minutes'  Oxygen 

Absorption. 

Description  of  Sample. 

Grains  per  Gallon. 

Putresci- 
bility. 

Before  In- 

After  In- 

cubation. 

cubation. 

Raw  sewage 

4'24 

7-00 

_ 

Raw  sewage  containing  waste 

acid 

dfo8 

A'AA 

-f 

Raw  sewage  containing  waste 

t  wij 

*T  T^T" 

tar  products  

5f98 

5'54 

+ 

Open  septic  tank  effluent 

2-66 

4*97 

_ 

Effluent  from  £-acre  bacteria 

bed,  early  stage  of  working... 

1-62 

1-62 

X 

Effluent   from  £-acre  bacteria 

bed,  later  stage  of  working  ... 

77 

•65 

+ 

Effluent  from  experimental  bac- 

teria bed,  second  contact  ... 

•14* 

•20 

+ 

Effluent  from  experimental  bac- 

teria bed,  second  contact  ... 

•18* 

•18 

+ 

Ship  canal  water  (dry  weather) 

i  -08 

1*64 

Ship  canal  water  (wet  weather) 

•24 

•16 

+ 

Note :—  +   indicates  non-putrefactive. 
-   indicates  putrefactive. 
X  indicates  questionable. 

*  In  these  two  cases  nitrites  were  present  after  incubation, 
equivalent  to  -04  and  -06  respectively.  After  treatment  with  urea 
the  numbers  after  incubation  would  therefore  be  -16  and  -12. 


38          SEWAGE  WORKS  ANALYSES 


CHAPTER  III. 
THE   DETERMINATION   OF   AMMONIA. 

THE  majority  of  organic  substances  occurring  in 
sewage  contain  nitrogen,  which  can  in  various 
ways  be  determined  in  the  form  of  ammonia. 

One  of  the  chief  nitrogenous  substances  in 
sewage  is  urea  or  carbamide,  CO(NH2)2,  which 
is  a  normal  constituent  of  urine.  By  the  action 
of  an  organism  (micrococcus  urei)  which  is  always 
present  in  urine  the  urea  is  rapidly  converted  into 
ammonium  carbonate  thus  : — 

CO(NH2)2+2H2O  =  (NH4)2CO3. 

A  certain  amount  of  ammonium  carbonate  is 
therefore  always  to  be  found  in  sewage,  and  it 
rapidly  increases  in  quantity  if  the  sewage  is 
allowed  to  stand  some  time  before  analysis.  It 
can  easily  be  driven  off  by  boiling,  and  constitutes 
the  main  source  of  what  is  generally  spoken  of  as 
free  ammonia. 

Some  of  the  nitrogen  in  sewage  occurs  in  such 
compounds  as — 

Glycocoll  (amido-acetic  acid,         V    2       2 ) 

COOH   / 

.,    C5Hi0NH2\ 
Leucine  (amido-isocaproic  acid,    I  nni4.       ) 


SEWAGE   WORKS   ANALYSES.         39 

Asparagin  (amido-succinamic  acid, 

CH2CONH2 
CH(NH2)COOH 

These  substances  and  others  of  an   allied  but 

more  complex  composition  yield  ammonium  salts 

of  the  corresponding  acids  on  putrefaction.  Thus — 

CHNH2+ H2O  =  CH3COONH4 

COOH  (ammonium  acetate). 

Such  ammonia  is  also  in  part  given  off  on 
boiling,  especially  with  addition  of  a  little  sodium 
carbonate. 

The  addition  of  sodium  carbonate  when  boiling 
off  the  "  free  "  ammonia  also  neutralises  any  acids 
present  in  the  sewage  from  manufacturing  pro- 
cesses, which  otherwise  might  combine  with  some 
of  the  "free"  ammonia  to  form  fixed  salts,  and 
thus  prevent  its  evolution  on  boiling.  The  total 
ammonia  given  off  on  boiling  with  sodium  carbo- 
nate is  therefore  sometimes  described  as  free  and 
saline  ammonia. 

The  above  compounds  and  others,  e.g.,  uric 
acid,  and  bodies  of  an  albuminous  character,  such 
as  proteids,  etc.,  yield  ammonia  at  once  on  boiling 
with  a  strongly  alkaline  solution  of  potassium 
permanganate. 

The  ammonia  thus  obtained,  as  it  is  derived 
in  part  from  albuminoid  substances,  is  generally 
spoken  of  as  albuminoid  ammonia.* 

The  increase  of  free  ammonia  at  the  expense  of 
albuminoid    ammonia,   which   is  observed  when 
*  Wanklyn  &  Chapman,  "  Water  Analysis." 


40          SEWAGE   WORKS   ANALYSES. 

sewage  is  allowed  to  stand,  is  due  to  the  conversion 
of  the  above  substances,  together  with  urea,  into 
ammonia  salts  by  the  action  of  the  organisms 
present  in  the  sewage.  These  and  similar  changes 
probably  occur  in  the  early  stages  of  working 
bacteria  beds,  referred  to  on  p.  57. 

A  further  quantity  of  ammonia  can  be  obtained 
when  sewage  is  heated  for  some  time  with  strong 
sulphuric  acid  and  then  neutralised  and  distilled 
with  caustic  soda.  This  is  generally  termed 
organic  ammonia,  and  is  derived  from  such  sub- 
stances as  are  not  broken  up  by  the  methods  used 
for  determining  free  and  albuminoid  ammonia.* 

The  quantitative  estimation  of  the  ammonia 
evolved  by  either  of  the  foregoing  methods  of 
treatment  is  effected  by  NESSLERISATION.  This 
process  is  based  on  the  following  reaction  : — 

When  an  alkaline  solution  of  mercuric  iodide  is 
added  to  a  solution  containing  ammonia,  a  brown 
precipitate  is  formed.  If  the  ammonia  is  present 
in  small  quantities,  a  brown  coloration  only  is 
produced,  the  depth  of  colour  depending  on  the 
quantity  of  ammonia  present.  The  brown  pre- 
cipitate is  generally  considered  to  have  the  formula 
NHgaI,  H20. 

By  comparing  the  tint  given  by  the  ammonia  in 
the  sample  to  be  analysed  with  a  series  of  standard 
tints  produced  by  adding  Nessler  reagent  to  known 
quantities  of  ammonia,  the  amount  of  ammonia 
present  in  the  sample  can  be  determined. 

*  SeeRideal  ''Sewage  and  Sewage  Purification,"  Chap.  V. 


SEWAGE   WORKS  ANALYSES.         41 

For  the  complete  process  of  distillation  and 
Nesslerisation,  the  following  apparatus  and  solu- 
tions are  necessary : — 

SOLUTIONS. 

Nessler  Reagent. — 62*5  grms.  potassium  iodide  are 
dissolved  in  about  250  c.c.  distilled  water,  10  c.c. 
of  this  solution  are  set  aside,  and  into  the  re- 
mainder is  carefully  run  a  cold  saturated  solution  of 
mercuric  chloride.  A  brilliant  red  precipitate  of 
mercuric  iodide  forms,  and  at  first  quickly  redis- 
solves  on  shaking.  The  addition  is  continued  till 
a  permanent  precipitate  forms.  This  is  redissolved 
by  the  potassium  iodide  held  in  reserve,  and  more 
mercuric  chloride  is  added  drop  by  drop  until 
after  stirring  a  slight  red  opalescence  remains ; 
150  grms.  of  caustic  potash  are  dissolved  in  dis- 
tilled water,  allowed  to  cool  and  added  gradually 
with  continued  shaking,  to  the  opalescent  solution. 
The  whole  is  made  up  to  I  litre,  allowed  to  settle, 
and  the  clear  liquid  decanted  into  a  bottle. 

The  Nessler  solution  improves  on  keeping,  hence 
it  should  be  made  up  some  time  before  it  is 
required.  Special  attention  must  be  given  to  the 
end  point  of  the  addition  of  mercuric  chloride  to 
the  iodide  solution.  If  the  potassium  iodide  be  in 
excess,  the  Nessler  will  not  be  delicate,  and  the 
colour  with  ammonia  will  be  long  in  reaching  full 
density.  On  the  other  hand,  the  addition  of  an 
excess  of  mercuric  chloride  will  give  an  excess  of 
mercuric  iodide,  which  will  dissolve  when  the 


42  SEWAGE   WORKS   ANALYSES. 

potassium  hydrate  is  added,  and  the  Nessler  will 
be  excessively  delicate,  the  colour  striking  full 
rapidly ;  but  it  is  liable,  after  the  ammonia  tubes 
have  stood  about  ten  minutes,  or  even  less,  to 
become  turbid  and  deposit  a  red  crystalline 
precipitate,  so  that,  whilst  maximum  delicacy  is 
required,  this  turbidity  is  to  be  avoided.  Prac- 
tice is  the  only  guide  to.  making  a  good  Nessler 
solution.  One  c.c.  of  Nessler  solution  ought  to 
show  colour  with  opoo8  mgm.  NH3  (0*8  c.c.  of 
the  centinormal  ammonium  chloride  solution  in 
50  c.c.  pure  water). 

Stick  potash  is  best  dissolved  in  water  in  an 
earthenware  basin.  Thin  glass  vessels  are  apt  to 
crack  during  the  operation. 

Ammonia-free  Water. — This  is  best  obtained  in 
quantity  by  distilling  from  a  tin  or  copper  still, 
rejecting  the  distillate  until  it  is  free  from  ammonia 
when  tested  with  the  Nessler  reagent.  About  one 
quarter  of  the  original  volume  should  be  left  in 
the  still  after  each  distillation,  and  the  last  50  c.c. 
of  the  portion  collected  should  be  tested  to  see 
that  it  is  free  from  ammonia.  The  still  must  be 
frequently  cleaned,  or  organic  matter  will  accumu- 
late in  the  residue. 

Sodium  Carbonate. — 100  grms.  of  dry  sodium 
carbonate,  Na2COs  are  dissolved  in  a  litre  of  water, 
the  solution  filtered  and  boiled  till  50  c.c.  fail  to 
show  any  indication  of  the  presence  of  ammonia 
when  tested  with  Nessler  reagent. 

Alkaline  Potassium  Permanganate. — This  is  best 


SEWAGE   WORKS  ANALYSES.         43 

made  up  in  quantities  of  3  litres  ;  24  grms.  of 
potassium  permanganate  are  dissolved  in  about 
500  c.c.  of  tap  water,  600  grms.  of  potash  are 
separately  dissolved,  and  the  solutions  mixed  and 
thoroughly  boiled  in  a  flask.  This  is  best  done  in 
quantities  not  exceeding  a  litre  (in  case  of  breakage). 
The  boiled  solutions  are  then  mixed  and  made  up 
to  3  litres  with  distilled  water  free  from  ammonia. 

Standard  Ammonium  Chloride. — This  should  be 
made  up  with  the  greatest  care,  as  one  litre  will 
last  a  long  while,  and  the  accuracy  of  a  large 
number  of  determinations  will  depend  upon  the 
correctness  of  the  standard  solution. 

The  ammonium  chloride  as  ordinarily  obtained 
should  be  purified  by  sublimation.  For  this  pur- 
pose a  few  grms.  are  heated  in  a  porcelain  dish  on 
a  sandbath  over  which  a  large  glass  funnel  is 
inverted.  The  salt  sublimes  and  condenses  on 
the  inner  side  of  the  funnel  in  a  powdery  condition. 
Only  the  whitest  portions  of  the  sublimate  should 
be  taken  for  solution. 

3*15  grms.  of  the  purified  salt  are  dissolved  in 
a  litre  of  ammonia-free  water.  The  temperature  of 
the  water  should  be  carefully  adjusted  to  be  equal  to 
that  for  which  the  litre  flask  is  graduated  (usually 
15°  C.)  as  there  is  considerable  reduction  of  tempera- 
ture when  ammonium  chloride  dissolves  in  water. 

One  c.c.  of  the  solution  contains  i  mgm. 
ammonia.* 

*  If  3'82i5  grms.  ammonium  chloride  are  taken,  each  c. 
contains  i  mgm.  nitrogen. 


c. 


44          SEWAGE   WORKS   ANALYSES. 

For  general  use  more  dilute  solutions  should  be 
made  from  this  normal  standard  solution. 

Decinormal  Solution. — 100  c.c.  of  the  normal 
solution  are  diluted  to  i  litre.  One  c.c.  of  this 
solution  contains  'i  mgm.  ammonia. 

Centinormal  Solution. — 100  c.c.  of  the  decinormal 
solution  are  diluted  to  i  litre.  One  c.c.  of  this 
solution  contains  *oi  mgm.  ammonia. 

In  making  these  dilutions,  care  must  be  taken 
that  the  liquid  at  the  time  of  measurement  has  a 
temperature  equal  to  the  graduation  temperature 
of  the  flask. 

The  following  is  Mr.  Scudder's  description  of 
the  estimation  of  ammonia  as  carried  out  in  the 
laboratory  of  the  Mersey  and  Irwell  Joint 
Committee : — 

"The  distillation  is  carried  out  in  32-02.  round- 
bottomed  Bohemian  flasks.  The  condenser  tubes 
are  made  of  block  tin,  placed  in  a  copper  box, 
through  which  a  stream  of  water  passes,  so  as  to 
ensure  that  the  distillates  are  of  a  constant 
temperature,  which  is  a  most  important  point  to 
observe  when  Nesslerising.  700  c.c.  of  distilled 
water  are  placed  in  the  flask,  i  c.c.  Na2COa  solu- 
tion added  and  50  c.c.  distilled  over  and  tested  for 
ammonia.  If  not  quite  free,  a  second  50  c.c.  is 
distilled  (this  second  50  is  invariably  free).  The 
flask  is  allowed  to  cool,  and  a  measured  quantity 
of  the  sewage  effluent  is  added,  varying  from  10  c.c. 
to  70  c.c.,  according  to  whether  the  effluent  is 
crude  sewage,  tank  effluent,  or  filtered  effluent. 


SEWAGE  WORKS  ANALYSES.         45 

The  flask  is  connected  with  the  condenser,  and 
250  c.c.  distilled  over  and  collected  in  a  250-c.c 
flask  for  estimation  of  free  and  saline  ammonia ;  a 
final  portion  of  50  c.c.  is  next  distilled  into  a 
Nessler  tube  and  tested  for  ammonia  ;  but  almost 
invariably  it  is  found  to  be  free. 

"  Whilst  the  distillation  has  been  going  on,  50  c.c. 
of  the  alkaline  permanganate  are  put  into  a 
nickel  basin  with  20  c.c.  distilled  water  and 
boiled  for  a  few  minutes  to  expel  any  ammonia ; 
50  c.c.  of  the  alkaline  permanganate  (previously 
boiled)  is  then  added  to  the  flask,  and  the 
distillation  continued,  the  distillate  being  col- 
lected in  a  loo-c.c.  flask,  then  in  5o-c.c.  Nessler 
tubes,  until  250  c.c.  of  distillate  have  been 
collected. 

"  It  is  important  to  observe  the  rate  at  which  the 
albuminoid  ammonia  forms,  and  this  is  recorded 
in  the  note-book  (see  examples  to  follow). 


"  NESSLERISING. 

"  Twelve  Nessler  glasses  are  chosen  having  the 
50  c.c.  mark  at  least  4!  inches  from  the  bottom. 
Each  glass  in  the  set  must  have  the  50  c.c.  mark  at 
exactly  the  same  height.  These  glasses  are  kept 
specially  for  standards.  For  all  other  purposes 
tubes  6  in.  x  i  in.  (preparation  tubes),  with  a  file 
mark  at  50  c.c.,  are  found  useful  and  cheaper  than 
Nessler  glasses. 

"  When  much  work  has  to  be  done  it  is  convenient 


46          SEWAGE   WORKS  ANALYSES. 

to  have  pieces  of  wood  g  in.  x  ij  in.  x  i  in.  with 
five  holes  to  fit  the  tubes,  so  that  the  tubes  can 
all  stand  in  proper  order  and  without  danger  of 
falling. 

"  The  standard  tubes  are  held  in  a  piece  of  wood, 
g  in.  x  7  in.  x  ij  in.,  containing  twelve  holes. 

"Procedure. — Measure  out  into  a  preparation  tube 
part  of  the  250  c.c.  distillate  containing  the  free 
and  saline  ammonia,  also  a  part  of  the  100  c.c. 
albuminoid  ammonia  distillate — the  amounts  to 
be  taken  vary  so  much  with  sewage  effluents  that 
experience  alone  can  guide.  When  measured  out 
make  all  up  to  the  50  c.c.  mark.  The  standards 
are  now  prepared  by  measuring  out  known  amounts 
of  the  standard  centinormal  ammonium  chloride. 
The  standards  used  are  0*5  c.c.,  i  c.c.,  and  so  on, 
increasing  by  o'5  c.c.  up  to  5'5  c.c.,  or  eleven  in  all. 
The  tubes  are  then  made  up  to  the  50  c.c.  mark 
with  distilled  water ;  i  c.c.  Nessler  solution  is 
now  added  to  all  the  tubes,  mixed  and  allowed  to 
stand  five  minutes,  so  that  the  colour  may  fully 
develop.  If  any  fraction  of  the  distillate  is  seen 
to  be  too  deep  in  colour,  or  shows  no  colour  in 
half  a  minute,  it  is  better  to  take  larger  or  smaller 
fractions  from  the  bulk.  After  five  minutes  the 
spare  tube  of  the  set  of  twelve  Nessler  glasses  is 
taken  and  the  contents  of  the  first  preparation 
tube  emptied  into  it  and  compared  with  the 
standards. 

"A  piece  of  white  filter-paper  should  be  placed  on 
the  bench,  and  the  colour  observed  by  looking 


SEWAGE   WORKS   ANALYSES.         47 

down  through  the  tube  to  the  white  surface.  (A 
piece  of  filter-paper,  6  in.  x  6  in.,  gives  a  finer 
white  surface  than  a  glazed  plate.) 

"  If  the  tube  does  not  match  any  standard  exactly, 
but  lies  between  two,  the  difference  must  be  judged 
by  putting  the  tube  between  the  standards  above 
and  below,  and  comparing  the  three. 

"  Some  observers  can  note  a  small  difference  of 
this  kind  more  easily  by  looking  through  the 
meniscus  from  the  side.  When  the  number  has 
been  fixed,  it  is  noted.  The  Nessler  glass  is  then 
emptied  and  the  contents  of  the  next  preparation 
tube  poured  into  it. 

"  By  carrying  out  this  method  the  highest  accu- 
racy is  obtained  with  the  smallest  number  of 
Nessler  glasses.  A  full  range  of  standards  is  pre- 
pared at  the  same  time  as  the  test  liquids,  and  all 
stand  under  the  same  conditions. 

"The  maximum  colour  that  can  be  compared 
with  accuracy  by  this  method  must  not  exceed 
that  produced  by  5*5  c.c.of  the  standard  ammonium 
chloride  solution. 

"  Examples  from  laboratory  note-book : — 

i.  A  bad  effluent,  25  c.c.  taken  for  analysis. 
A.  Free  and  Saline  Ammonia. 
Distillate  250  c.c.=  52*5  c.c.  NH4C1.  solution 
(ioc.c.=  2*1). 
Next  50  c.c.  =  o'o 
Total  =  52*5 
As  25  :  70  :  :  52-5  =  52-5  X  2'8  = 

147-00  c.c.  NH4C1.  =  1-47  grains  per  gallon. 


48          SEWAGE   WORKS  ANALYSES. 

B.  Albuminoid  ammonia. 
Distillate  100  c.c.  =  9-4  c.c.  NH4C1  solution 
(50  c.c.  =  47). 

Next  50  c.c.  =  2*8  c.c.   NH4C1    solution 
„    50  c.c.  =  1-8  c.c.        „  „ 

„    50  c.c.  =  1*5  c.c.        „  „ 

Total  =    15-5 

(Next  50  c.c.  =  ri  not  included.) 
As  25  :  70  ::  15-5  =  15-5  X  2'8  = 
43*4  c.c.  NH4C1  =  0*434  grains  per  gallon. 
2.  A  fair  effluent,  50  c.c.  taken  for  analysis. 

A.  Free  and  saline  ammonia. 

Distillate  250  c.c.  =  70*0  c.c.  NH4C1  solution 
(IOC.G.  =  2*8). 
Next  .50  c.c.  =  Q'o 
Total  =  70*0 

As  50  :  70  : :  70  =  70  x  1*4  =  98  c.c.  NH4C1 
=  0*98  grains  per  gallon. 

B.  Albuminoid  ammonia. 

Distillate  100  c.c.  =  4*8  c.c.   NH4C1  solution 
(50  c.c.  =  2-4). 
Next  50  c.c.  =  ri  c.c. 
„    50  c.c.  =  0-6  c.c. 
,,    50  c.c.  =  Q'o 

Total  =  6-5  x  1-4  =  9-1  c.c.  NH4C1 
=  •091  grains  per 
gallon." 

The  following  is  a  description  of  the  apparatus 
and  methods  employed  in  the  Manchester  Cor- 
poration Sewage  Works  laboratory  : — 


SEWAGE    WORKS   ANALYSES.         49 

Description  of  Apparatus. — For  making  a  number 
of  distillations  the  apparatus  shown  in  Fig.  3  has 
been  found  satisfactory. 

A  rectangular  sheet  iron  tank,  Fig.  3,  is  fitted 
with  six  vertical  bulbed  condensers.  The  upper 
ends  of  these  are  connected  with  six  ordinary  flasks 
of  about  one  litre  capacity  (32  ozs.),  while  the 
lower  ends  dip  into  glass  jars  or  cylinders  in  which 
the  ammoniacal  distillate  can  be  collected.  A  con- 
stant stream  of  water  circulates  through  the  tank. 

The  particulars  of  construction  of  the  condensing 
apparatus  are  as  follows  : — 

The  rectangular  tank  measures  two  feet  in 
length,  thirteen  inches  in  breadth,  and  twelve 
inches  in  height.  The  water  is  brought  in  by  a 
tube  reaching  to  the  bottom  of  the  tank  at  one 
corner,  and  is  taken  off  at  the  upper  and  diagonally 
opposite  corner,  so  that  the  heated  water  is  regu- 
larly displaced  throughout  the  tank.  The  tank  is 
supported  on  a  strong  iron  stand  of  corresponding 
length  and  breadth,  and  ten  inches  in  height.  Three 
detachable  stays  are  fitted  at  regular  intervals 
across  the  top  of  the  tank,  pierced  with  holes  at  each 
side  to  receive  the  glass  condenser  tubes.  Flanged 
holes  are  correspondingly  placed  in  the  bottom  of 
the  tank,  and  the  tubes  are  fixed  watertight  into 
these  with  collars  of  wide  indiarubber  tubing. 

The  outside  diameter  of  the  tubes  is  half  an  inch, 
the  diameter  of  the  holes  three-quarters  of  an  inch. 

The  total  length  of  each  tube  is  twenty  inches, 
and  there  are  four  bulbs  on  each  tube,  one  inch  in 

s.w.  E 


50          SEWAGE   WORKS  ANALYSES. 

diameter.  The  bulbs  are  two  inches  apart  and 
five  inches  from  the  ends  of  the  tubes.  The  bore 
of  the  exit  tubes  from  the  flasks  being  only  slightly 
less  than  that  of  the  condenser  tube,  the  joint  is 
easily  made  by  a  piece  of  indiarubber  tubing  which 
fills  the  annular  interspace. 

Stokes'  Colorimeter. — This  instrument  is  shown  in 
Fig.  4.  It  consists  essentially  of  two  glass  cylin- 
ders, 100  c.c.  capacity,  joined  at  the  base  by  an 
indiarubber  tube. 

One  of  the  cylinders  is  graduated  into  c.c.,  and 
can  slide  in  a  clamp  which  is  attached  to  a  vertical 
brass  support.  The  second  cylinder  rests  on  a 
sloping  glass  plate,  beneath  which  is  a  piece  of 
white  opal  glass, 

In  these  two  cylinders  is  placed  a  known  amount 
of  ammonia.  For  this  purpose  *5  mgm.  is  generally 
taken,  i.e.,  5  c.c.  of  the  decinormal  ammonium 
chloride  solution  (i  c.c.  =  'i  mgm.  NH3),  and 
diluted  to  100  c.c.  with  ammonia-free  water ;  4  c.c. 
of  Nessler  solution  are  added,  and  the  mixture  is 
poured  into  the  colorimeter. 

When  the  cylinders  are  level  with  one  another, 
the  liquid  stands  at  the  50  mark. 

A  third  cylinder  is  taken  of  such  dimensions  that 
•25  mgm.  ammonia  dissolved  in  50  c.c.  ammonia- 
free  water,  together  with  2  c.c.  Nessler  solu- 
tion, gives  a  coloration  exactly  equal  to  the 
standard  when  the  reading  on  the  graduated  tube 
is  50.  This  standard  cylinder  is  always  used  for 
making  the  comparative  colour  tests. 


FIG.  4.— THE.  STOKES'    COLORIMETER 


[To  face  page  50. 


f  0V  THE 

{  UNIVERSITY 

V          OF 

X£A 


SEWAGE   WORKS   ANALYSES.         51 

Fifty  or  100  c.c.  of  the  ammonia  distillate, 
according  to  the  amount  of  ammonia  likely  to 
be  present,  are  taken,  and  2  or  4  c.c.  Nessler 
reagent  added,  and  the  mixture  allowed  to  stand 
at  least  ten  minutes  in  order  to  attain  the  room 
temperature,  and  for  the  depth  of  tint  to  reach 
a  maximum.  The  coloured  solution  is  then  poured 
into  the  standard  cylinder,  which  is  placed  on  the 
glass  plate.  The  graduated  cylinder  of  the  instru- 
ment is  then  moved  up  and  down  until  the  tints 
in  the  plain  cylinder  of  the  instrument  and  the 
standard  cylinder  correspond.  This  identity  of 
tint  is  best  judged  by  observing  the  cylinders 
through  a  card  perforated  with  two  holes  about 
half  an  inch  in  diameter,  coinciding  with  each 
cylinder.  A  good  light  should  be  directed  on  to 
the  plate  of  opal  glass  beneath  the  cylinders. 

The  level  of  the  liquid  in  the  standard  cylinder 
is  then  read.  From  this  reading  the  amount  of 
ammonia  in  the  cylinder  examined  can  be  calcu- 
lated thus  : — 

Supposing  the  reading  to  be,  for  example,  64, 
and  the  amount  of  ammonia  in  the  two  connected 
cylinders  to  be  *5  mgm.,  then  the  amount  corre- 
sponding to  the  cylinder  to  be  tested  will  be 

100  —  64  .  0 

5  X  5  =   18  mgm. 

100 

When  the  amount  of  ammonia  distilled  over 
from  the  sample  is  large  it  should  be  made 
up  to  a  known  quantity,  and  a  given  proportion 
taken. 

E  2 


52          SEWAGE  WORKS  ANALYSES. 

The  standard  solution  in  the  colorimeter  should 
be  made  up  afresh  about  every  four  hours,  to 
avoid  possible  changes,  although  experiment  has 
shown  that  little,  if  any,  change  takes  place  in 
eight  hours. 

DETERMINATION    OF   FREE  AND    SALINE  AMMONIA. 

The  quantity  of  the  sample  taken  varies  with 
the  amount  of  impurity  present :  for  sewage  and 
tank  effluents,  35  c.c.,  for  filtrates,  70  or  140  c.c., 
are  taken.  The  35  c.c.  are  diluted  with  500  c.c. 
of  tap-water*  and  a  few  drops  of  Na2COs  solution 
added ;  200  c.c.  are  then  distilled  off  into  glass 
jars  containing  a  layer  of  ammonia-free  water, 
into  the  end  of  which  the  condenser  dips.  The 
solution  of  ammonia  thus  obtained  is  made  up 
to  250  c.c.,  and  50  c.c.  taken  and  Nesslerised. 

Example.     35  c.c.  of  sample  taken. 

Reading  of  colorimeter  =  45. 

TOO  •—  4"?    X   "5  •       •       ,r 

— — — 53, 5  =  mgm.  ammonia  in  the 

50  c.c.   of  distillate 
taken. 

=  '275- 

*275  X  5  =  mgm.  ammonia  in 
250  c.c.  of  distillate, 
i.e.,  in  35  c.c.  of 
sample. 

=  i'375« 

*  Manchester  tap-water  contains  very  little  ammonia.  The 
water  used  should  in  all  cases  be  carefully  analysed  from 
time  to  time  and  allowance  made  for  any  ammonia  present. 


SEWAGE  WORKS  ANALYSES.         53 

1*375  X  2  =  mgm.  ammonia  in 
70  c.c.  sample,  i.e., 
grains  ammonia  per 
gallon  of  sample. 

=  275- 

From  the  above  calculation  it  can  be  seen  that 
the  grains  per  gallon  of  ammonia  are  readily 
arrived  at  by  the  following  simple  calculations : — 

If  35  c.c.  of  the  sample  are  taken,  then 
IPO  -  reading  of  colorimeter  =       .  s  per  gallon 

2O 

ammonia. 

If  70  c.c.  of  the  sample  are  taken,  then 
IPO  -  reading  of  colorimeter  =  grains  pef  gallon 

4°  ammonia. 

DETERMINATION   OF  ALBUMINOID   AMMONIA. 

This  is  determined  by  adding  50  c.c.  of  alkaline 
permanganate  to  the  liquid  from  which  the  free 
ammonia  has  been  expelled,  together  with  100  c.c. 
of  tap-water,  and  distilling  off  150  c.c.  in  portions 
of  100  c.c.  and  50  c.c.,  and  collecting  in  "  Nessler 
glasses  "  of  these  dimensions. 

The  amount  of  ammonia  present  in  each  Nessler 
glass  is  determined  by  Nesslerisation* 

If  the  amount  of  ammonia  contained  in  the  last 
50  c.c.  of  distillate  is  large,  it  may  be  necessary  to 
distil  a  third  lot  of  50  c.c. ;  or  a  small  correction, 
determined  by  experience,  can  be  made  equivalent 
to  the  amount  still  left  in  the  sample. 

If  the  amount  of  ammonia  in  the  second  or 


54          SEWAGE   WORKS   ANALYSES. 

third  distillates  is  too  small  to  be  conveniently 
determined  by  the  colorimeter,  a  subsidiary 
standard  may  be  made  as  follows :  A  50  c.c. 
Nessler  glass  is  graduated  by  pasting  a  paper 
strip  on  the  outside.  This  should  extend  above 
the  50  c.c.  mark  to  the  level  reached  when  the 
volume  of  liquid  is  increased  by  2  c.c.  The  total 
height  corresponding  to  52  c.c.  may  then  be 
divided  into  five  equal  parts  ;  5  c.c.  of  the 
centinormal  ammonium  chloride  solution — i.e.,  '05 
mgm.  NH3 — are  added  to  the  glass,  made  up  to 
50  c.c.  with  ammonia-free  water  and  2  c.c.  of 
Nessler  solution  added. 

The  50  c.c.  of  distillate  to  be  tested  are  mixed 
with  2  c.c.  of  Nessler  solution,  and  the  tint  pro- 
duced compared  with  the  standard  just  described, 
by  placing  the  two  Nessler  glasses  (which  should 
be  of  the  same  dimensions)  side  by  side,  and 
looking  down  through  the  solutions  at  a  piece 
of  white  paper.  If  the  tint  in  the  sample  is  paler 
than  the  standard  solution,  the  latter  may  be 
poured  into  a  third  Nessler  glass  until  the  depth 
of  tint  in  the  two  cylinders  is  equal.  The  number 
of  divisions  or  parts  of  a  division  at  which  the 
liquid  now  stands  on  the  scale  is  then  read. 
Quantities  of  ammonia  greater  than  "05  mgm. 
can  easily  be  read  on  the  "  Stokes  "  instrument. 

Example : — 

The  total  quantity  of  albuminoid  ammonia  is 
calculated  as  follows  : — 

•35  c.c.  of  sewage  taken. 


SEWAGE   WORKS  ANALYSES.         55 

First  distillate  100  c.c.  gives  reading  on  the 
"  Stokes  "  instrument  40. 

Then  ammonia  in  first  distillate  =  --  — 

100 

=  '30  mgm. 

Ammonia  in  second  distillate  gives  reading  on 
the  "  Stokes"  instrument  88. 

Then  ammonia  in  second  distillate  =  -  - 

100 

=  •06. 

Ammonia  in  third  distillate  =  3  divisions  on  sub- 
sidiary scale  =  '03  mgm. 

The  total  ammonia  determined  in  35  c.c.  of  the 
sample  will  therefore  be  — 

•30  +  -06  +  -03  =  -39. 

To  this  should  be  added  '015,  the  amount  which 
experience  shows  will,  as  a  rule,  be  contained  in 
the  next  50  c.c.  if  distillation  is  continued,  the 
amount  of  ammonia  in  the  last  distillates  gene- 
rally decreasing  by  50  per  cent,  in  each  50  c.c. 
A  further  small  correction  must  be  made  for  the 
amount  of  albuminoid  ammonia  given  off  when 
500  c.c.  of  Manchester  tap  water  is  distilled  with 
alkaline  permanganate;  this  is  taken  at  "025  mgm. 

The  total  amount  of  ammonia  present  in  the 
35  c.c.  of  sewage  will  therefore  be  — 


In  70  c.c.  the  quantity  will  be  doubled,  i.e.,  the 
number  of  grains  per  gallon  of  ammonia  in  the 
sewage  will  be  '76. 

This  calculation,  though  tedious  to  describe,  is 
quickly  made. 


SEWAGE   WORKS   ANALYSES. 


Continual  practice  renders  it  possible  to  judge 
of  quantities  of  ammonia,  in  the  last  distillates,  less 
in  amount  than  "05  mgm.  In  this  case  the  making 
of  a  subsidiary  standard  may  be  dispensed  with. 

The  use  of  the  "  Stokes  "  colorimeter,  and  the 
adoption  of  estimated  values  (based  on  experience) 
for  the  later  distillates,  renders  the  methods  used 
in  the  Manchester  Sewage  Works  laboratory 
rather  more  rapid  than  those  described  by  Mr. 
Scudder,  and  where  a  large  number  of  samples 


Free  and  Saline 
Ammonia. 

Albuminoid 
Ammonia. 

M.  &I. 
J.  C. 

M.  C. 

M.  &I. 
J.C. 

M.  C. 

1899 

1900 

I76 
I-87 

177 

i  '97 

•311 
*339 

•284 
'297 

derived  from  the  same  sewage  have  to  be  com- 
pared, the  results  are  entirely  satisfactory  for  the 
purpose. 

Mr.  Scudder's  methods,  on  the  other  hand,  serve 
to  more  sharply  distinguish  one  class  of  sample 
from  another,  as  he  finds  that  raw  sewage  or  im- 
perfectly purified  effluent  will  continue  to  give  off 
ammonia  almost  indefinitely  when  distilled  with 
alkaline  permanganate,  while  with  a  good  effluent 
there  is  a  well-defined  end  point. 

The  free  ammonia  determinations  give  almost 
identical  results  in  the  two  laboratories ;  the  albu- 
minoid ammonia  figures  tend  to  be  slightly  lower 


SEWAGE   WORKS   ANALYSES. 


57 


in  the  Manchester  Corporation  laboratory.  On 
the  previous  page  are  the  averages  of  the  numbers 
obtained  in  the  analysis  of  duplicate  samples  in  the 
years  1899  and  1900.  In  the  following  table  are 
given  some  examples  of  the  ammonia  numbers  in 
certain  typical  sewages  and  effluents. 


Grains  per  Gallon. 

Parts  per  100,000. 

Description  of  Sample. 

Free  and 

Albumi- 

Free and 

Albumi- 

Saline 

noid 

Saline 

noid 

Ammonia. 

Ammonia. 

Ammonia. 

Ammonia. 

Manchester  sewage  (average 

settled  sample)         

2*04 

•3* 

2-91 

*44 

Manchester  sewage  (average 

shaken  sample)         

2-08 

'50 

2'97 

70 

Sewage  (Lawrence,  Mass.)  ... 

3-46 

•68 

4'99 

•98 

Sewage  (Accrington)  
Open  septic  tank,  Manchester 

3'57 
2-03 

•315 
•36 

5'n 
2-90 

'45 
"Si 

Effluent    from    experimental 

bed,  first  contact     

•65 

•146 

'93 

•21 

Effluent    from    experimental 

bed,  second  contact  

•225 

•06 

'32 

'09 

The  following  examples  show  the  difference  in 
the  relation  between  the  ammonias  in  the  septic 
tank  effluent  and  the  filtered  effluent  before  and 
after  nitrification  has  become  active  in  the  bacteria 
bed. 


Grains  per  Gallon. 

Parts  per  100,000. 

Description  of  Sample. 

Free  and 

Albumi- 

Free and 

Albumi- 

Saline 

noid 

Saline 

noid 

Ammonia 

Ammonia. 

Ammonia. 

Ammonia. 

Septic  tank  effluent     

a'oo 

•31 

2  '86 

'44 

Bacteria  bed  effluent  (nitrifica- 

tion active)     

I'lO 

'12 

i  '57 

•ijr 

Septic  tank  effluent    
Bacteria  bed  effluent  (nitrifica- 

i'55 

'27 

2'2I 

'39 

tion  slight)      

i*75 

•16 

2-50 

•23 

58          SEWAGE   WORKS  ANALYSES. 

DETERMINATION    OF  ORGANIC   AMMONIA. 

This  is  best  determined  by  the  method  of 
Kjeldahl,  which  depends  on  the  fact  that  when 
nitrogenous  organic  matter  is  heated  with  concen- 
trated sulphuric  acid  it  is  broken  up,  the  whole 
of  the  nitrogen  being  converted  into  ammonium 
sulphate.  On  making  alkaline,  the  ammonia  can 
be  distilled  over  and  Nesslerised. 

For  the  purpose  of  the  estimation  30  c.c.  of  the 
sample  may  be  conveniently  taken.  This,  after  a 
small  addition  of  sodium  carbonate,  is  distilled 
with  steam  till  the  distillate  shows  no  indication 
of  free  ammonia. 

The  distillation  with  steam  is  carried  on  in  the 
apparatus  shown  in  Fig.  5. 

The  steam  is  generated  in  32-02.  flasks,  and 
passed  into  the  8-oz.  flask  containing  the  sample. 
This  flask  should  be  further  heated  by  a  Bunsen 
burner  to  prevent  the  steam  from  condensing 
in  it.  The  steam  and  the  distillate  from  the 
sample  are  condensed  in  the  small  tube  con- 
denser, of  a  similar  type  to  that  described  on 
p.  49,  but  containing  only  two  tubes. 

The  tank  is  eight  inches  square  and  twelve  inches 
high,  the  stand  ten  inches  high.  The  glass  tubes 
used  are  similar  to  those  in  the  larger  condenser. 

During  the  progress  of  the  distillation  the 
sample  is  concentrated  to  about  5  c.c.  This  is 
transferred  to  an  8-oz.  Jena  flask  with  a  long  neck  (a 
special  form  of  flask  is  made  for  this  determination), 


fc.^ir' 


SEWAGE   WORKS  ANALYSES.         59 

and  20  c.c.  pure  sulphuric  acid  (free  from  nitrogen, 
either  as  nitric  acid  or  ammonia)  added. 

The  mixture  is  heated  carefully  over  the  bare 
Bunsen  flame  (under  a  hood  with  a  good  draught) 
for  about  half-an-hour ;  a  little  phosphoric  anhy- 
dride (P2O5)  is  then  added  and  the  mixture  further 
heated  till  quite  clear.  After  allowing  to  cool 
somewhat  the  mixture  is  poured  into  about  200  c.c. 
of  water,  and  after  complete  cooling  made  up 
exactly  to  250  c.c. ;  50  c.c.  of  this  solution  are 
then  taken  and  made  alkaline  with  a  saturated 
solution  of  caustic  soda;  500  c.c.  of  tap-water 
are  added,  and  the  ammonia  distilled  off  and 
Nesslerised  in  lots  of  100  c.c. 

In  order  to  allow  for  any  ammonia  unavoidably 
present  in  the  reagents  or  apparatus,  a  control 
experiment  should  be  made,  taking  35  c.c.  of  dis- 
tilled water  and  repeating  the  above  process  from 
the  beginning.  The  amount  of  ammonia  found 
by  the  control  experiment  should  be  only  a  small 
fraction  of  that  present  in  the  sample. 

The  relation  between  the  organic  ammonia, 
determined  as  above,  and  the  "  albuminoid " 
ammonia,  has  been  found  to  vary  within  fairly 
wide  limits  with  different  samples. 

The  Kjeldahl  determination  in  all  cases  gives 
higher  values  than  are  obtained  by  distillation  with 
alkaline  permanganate. 

Further  investigation  is  needed  in  order  to 
determine  the  cause  and  extent  of  this  variation 
under  different  conditions. 


6o 


SEWAGE   WORKS  ANALYSES. 


The  following  examples  will,  however,  serve  to 
give  some  idea  of  the  differences  likely  to  be  met 
with. 

The  numbers  given  for  the  Kjeldahl  deter- 
mination include,  in  all  cases,  the  " albuminoid" 
ammonia. 


Description  of  Sample. 

Organic  Ammonia. 

Albuminoid  Ammonia. 

Grains  per 
Gallon. 

Parts  per 
100,000. 

Grains  per 
Gallon. 

Parts  per 
100,000, 

Sewage    ...        ...        ...        ... 

iX-38 
1-62 

1-24 
1-32 

•85 

1-97 
2-31 

177 
1-88 

•86 

•23 
•32 

1-23 
73 

"33 
'59 

46 

Sewage    

Open  septic  tank  effluent 
Open     septic     tank    effluent 
(filtered  through  paper)     ... 
Open  septic  tank  effluent      ... 
Open     septic     tank    effluent 
(filtered  through  paper)     ... 

SEWAGE   WORKS  ANALYSES.         61 


CHAPTER   IV. 

THE    DETERMINATION   OF    NITRITES 
AND   NITRATES. 

THE  final  product  of  the  "oxidation  of  the  nitro- 
gen of  sewage  is  nitric  acid.  The  process  of  con- 
version of  ammoniacal  nitrogen  into  nitric  acid  is 
known  as  nitrification,  and  is  brought  about  by 
specific  micro-organisms. 

The  greater  part  of  the  sodium  nitrate  (Chili 
saltpetre,  nitrate  of  soda)  and  potassium  nitrate 
(saltpetre,  nitre)  of  commerce  has  probably  been 
formed  by  such  nitrification  processes  in  recent 
or  geologic  times. 

The  process  of  nitrification  proceeds,  however, 
in  stages,  the  ammonia  being  first  oxidised  by  one 
set  of  organisms  to  nitrous  acid,  and  the  nitrous 
acid,  in  its  turn,  to  nitric  acid,  thus  :  — 


For  nitrification  to  proceed  it  is  necessary  that 
some  base  —  e.g.,  either  ammonia  or  lime  —  should 
be  present  to  combine  with  the  nitrous  or  nitric 
acid  as  formed. 

Another  group  of  organisms  have  the  power, 
in  presence  of  oxidisable  matter,  of  reducing 


62          SEWAGE   WORKS  ANALYSES. 

nitrates  to  nitrites,  and  these  again  can  be 
reduced  to  nitrogen,  or  even  ammonia,  by  still 
other  forms. 

Such  a  process  is  known  as  denitrification. 

A  purely  chemical  denitrification  process  may 
take  place  by  the  interaction  of  the  nitrous  acid, 
produced  as  above,  with  urea,  thus : — 

2HNO2  +  CO  (NH2)2  =  3H2O  +  2N2  +  CO2. 

All  these  processes  probably  go  on  simultaneously 
in  a  bacterial  filter  or  contact  bed,  the  pre- 
dominance of  nitrification  over  denitrification  de- 
pending, among  other  things,  on  the  efficiency 
of  aeration.  In  the  absence  of  sufficient  oxygen, 
denitrifying  changes  predominate. 

The  determination  of  nitrites  and  nitrates  is 
therefore  of  the  greatest  importance  in  controlling 
the  working  of  a  bacterial  filter. 

The  method  of  recording  the  results  obtained 
has  been  described  on  p.  17. 

THE   DETERMINATION   OF   NITRITES. 

As  nitrites  are  rapidly  developed  on  allowing 
a  sample  of  sewage  or  effluent  to  stand  in  contact 
with  air,  either  by  oxidation  of  ammonia  or  re- 
duction of  nitrates  already  present,  it  is  important 
that  this  determination  should  be  made  as  soon 
as  possible  after  the  collection  of  the  sample.  If 
the  lapse  of  some  time  is  unavoidable  before  the 
sample  can  be  analysed,  the  bottle  should  be  kept 
carefully  closed,  and  the  analysis  made  as  soon 
as  possible  after  opening,  and  at  the  same  time 


SEWAGE   WORKS  ANALYSES.         63 

as  the  nitrate  determination  is  made.  It  may 
happen,  if  the  nitrite  is  determined  some  time 
after  the  nitrate,  that  the  ratio  of  the  nitrite  to 
the  nitrate  may  be  quite  different  from  what  it  was 
when  the  sample  was  taken,  owing  to  the  rapid 
development  of  nitrite  on  standing. 

The  determination  of  nitrites  depends  on  the 
formation  of  a  pink  azo  dye  by  the  action  of 
nitrous  acid  on  a  mixture  of  naphthylamine  and 
sulphanilic  acid  (known  as  Griess-Ilosvay  reagent). 
The  depth  of  tint  varies  with  the  quantity  of 
nitrous  acid  present.  The  reaction  is  as  follows  : — 

C6H4NH2S03H   +  Ci0H7NH2  +   HNO2  = 

Amido-benzene,  sulphonic  a  naphthyl-  nitrous 

acid  (sulphanilic  acid).  amine.  acid. 

C6H4(S03H)N2C10H6NH2  +  2H2O, 

a  naphthylamine-azo-benzene  sulphonic  acid. 

For  the  determination  of  nitrites  the  following 
solutions  are  necessary : — 

Standard  Solution  of  Potassium  Nitrite. — This  is 
made  by  dissolving  rather  more  than  i  grm.  of 
potassium  nitrite  in  200  cc.  of  water,  and  titrating 
10  c.c.  with  standard  permanganate  and  sulphuric 
acid. 

The  nitrite  solution  should  be  diluted  with  a 
considerable  volume  of  boiled  distilled  water,  say 
100  c.c.  water  to  10  c.c.  nitrite  solution.  The  solu- 
tion is  first  acidified,  and  the  permanganate  then 
run  in  till  a  permanent  pink  colour  is  obtained. 

The  permanganate  and  sulphuric  acid  used  for 
determining  oxygen  absorption  may  be  utilised. 


64          SEWAGE   WORKS  ANALYSES. 

10  c.c.  KMnO4  =  5*31  mgm.  KNO2  =  ro6  mgm. 
NH3  =  -869  N. 

The  strength  of  the  nitrite  solution  thus  obtained 
is  adjusted  so  that  I  c.c.  contains  nitrogen  equi- 
valent to  i  mgm.  NH3  or  i  mgm.  N,  according  as 
the  results  are  to  be  expressed  as  ammonia  or 
nitrogen. 

This  solution  can  be  diluted  as  required.  For 
working  purposes  a  solution  containing  nitrogen 
equivalent  to  *oi  mgm.  NH3  per  c.c.  will  be  found 
convenient. 

It  is  not  advisable  to  keep  a  dilute  solution  for 
any  length  of  time,  as  it  rapidly  oxidises  ;  and 
even  the  stronger  solution  should  be  checked 
against  permanganate  at  frequent  intervals. 

The  solution  is  best  retained  in  a  number  of  small 
bottles,  which  should  be  kept  completely  filled  and 
in  a  dark  place  until  the  solution  is  required  for  use. 

Griess-Ilosvay  Solution. — This  is  prepared  by 
mixing  equal  parts  of  two  solutions  : — 

(a)  i     grm.     of    sulphanilic    acid     (C6H4NH2 
SO3H)  is  dissolved  in  147  grms.  of  glacial  acetic 
acid  and  285  c.c.  water.     This  is  best  done  by 
warming    the  sulphanilic  acid  with    the    glacial 
acetic,  to  which  an  equal  bulk  of  water  has  been 
added.     The  remaining  water   should    be   added 
carefully,  the  mixture  being  warmed  and  stirred 
to  keep  the  sulphanilic  acid  in  solution. 

(b)  o'2   grm.    a    naphthylamine    (CioH7NH2)  is 
dissolved    in    14*7    grm.  glacial    acetic  acid   and 
325  c.c.  water.     As  in  the  case  of  the  sulphanilic 


SEWAGE  WORKS   ANALYSES.         65 

acid,  the  naphthylamine  is  best  dissolved  by 
warming  first  with  the  acid,  to  which  about  twice 
its  volume  of  water  has  been  added,  (in  order  to 
prevent  formation  of  an  anilide  by  combination  of 
the  acid  and  the  naphthylamine,)  and  afterwards 
adding  the  remainder  of  the  water. 

The  greater  proportion  of  these  solutions  should 
be  kept  separately,  not  more  than  two  or  three 
days'  supply  of  the  mixture  (i.e.,  the  Griess-Ilosvay 
solution)  being  made  up  at  once,  as  it  tends  to 
turn  pink,  owing  to  development  of  nitrite  in  the 
solution  from  ammonia  in  the  air.  The  amount 
of  nitrite  is  determined  quantitatively  as  follows  : — 

Five  c.c.  of  the  standard  solution  of  KNO2 
(i  c.c.  =  *oi  mgm.  NH3)  are  made  up  to  50  c.c. 
in  a  small  Nessler  glass  with  distilled  water, 
and  2  c.c.  of  the  Griess-Ilosvay  solution  added; 
35  c.c.  of  the  sample  are  taken,  and  2  c.c.  of 
the  Griess-Ilosvay  solution  added. 

The  sample  is  then  transferred  to  a  50  c.c. 
Nessler  glass  of  equal  dimensions  with  the  one 
containing  the  standard  solution,  and  made  up  to 
52  c.c.  with  distilled  water. 

Both  standard  and  sample  are  allowed  to  stand 
for  fifteen  minutes  before  comparing  the  pink 
coloration  in  each.  The  depth  of  tint  is  then 
compared  by  pouring  out  either  the  standard 
solution  or  the  sample,  whichever  has  the  deeper 
tint,  until  the  columns  left  in  the  Nessler  glasses 
appear  of  equal  tint  on  looking  down  the  glass  at 
a  piece  of  white  paper.  If  a  paper  scale  is  gummed 

s.w.  F 


66         SEWAGE   WORKS   ANALYSES. 

on  to  the  Nessler  glasses,  as  in  the  determination 
of  small  quantities  of  ammonia  (see  p.  54),  the 
ratio  between  the  sample  and  the  standard  is  easily 
determined. 

Thus,  if  the  scale  is  divided  into  five  parts,  each 
part  =  *oi  NH3.  If  the  columns  are  equal  in  tint 
when  the  standard  stands  at  2,  this  indicates  that 
•02  nitrite  (expressed  in  terms  of  NH3)  is  present 
in  35  c.c.  of  the  sample,  i.e.,  "04  mgm.  in  70  c.c. 
or  '04  grains  NH3  per  gallon,  or  '03  grains  N  per 
gallon  if  the  nitrite  solution  has  been  adjusted  to 
give  results  in  terms  of  nitrogen. 

With  constant  practice  it  is  easy  to  estimate  at 
sight  with  sufficient  accuracy  the  quantities  of 
nitrite  corresponding  to  the  depth  of  tint. 

In  the  laboratory  of  the  Mersey  and  Irwell  Joint 
Committee  nitrites  are  determined  by  the  depth  of 
yellowish-brown  colour  produced  by  the  addition  of 
meta-phenylene-diamine  (C6H4(NH2)2).  The  results 
are  expressed  in  grains  of  nitrous  nitrogen  per  gallon. 

The  following  are  Mr.  Scudder's  notes  on  the 
method : — 

"ESTIMATION  OF  NITRITES. 

"  Standard  solutions  : — 

"  i.  Meta-phenylene-diamine. — Eight  grms.  of  the 
hydrochloride  of  this  base  are  dissolved  in  a  litre 
of  distilled  water,  and,  if  necessary,  decolourised 
by  animal  charcoal,  and  made  acid  with  hydro- 
chloric acid. 

"2.  Dilute  Sulphuric  Acid. — One  part  sulphuric 
acid  to  three  of  distilled  water.  The  solution  is 


SEWAGE   WORKS   ANALYSES.         67 

rendered  faintly  pink  by  the  addition  of  standard 
permanganate  of  potash  solution. 

"3.  Sodium  Nitrite. — Dissolve  no  grms.  of  silver 
nitrite  in  boiling  distilled  water,  and  add  a  pure 
solution  of  sodium  chloride  until  no  further  pre- 
cipitation of  silver  chloride  occurs.  Cool  and 
make  up  to  a  litre.  Allow  to  stand  twenty-four 
hours,  and  then  dilute  100  c.c.  of  the  clear  liquid 
to  a  litre  and  fill  into  6  or  8  oz.  stoppered  bottles, 
and  keep  them  in  the  dark. 

"  i  c.c.  sodium  nitrite  =  0*01  mgm.  nitrogen. 

"  Procediire  for  Testing. — The  test  is  made  with 
the  original  sewage  effluent  if  clear  enough,  but  in 
turbid  effluents  the  colour  must  be  removed  by 
shaking  the  effluent  with  a  little  alumina  ferric 
cake  and  allowing  it  to  settle.  10  c.c.,  25  c.c., 
and  50  c.c.  of  the  clear  effluent  are  measured  into 
Nessler  glasses  and  made  up  to  the  50  c.c.  mark 
with  distilled  water.  The  standards  are  made  up 
from  the  sodium  nitrite  solution,  using  exactly  the 
same  standards  as  in  ammonia  estimations.  All 
are  made  up  to  the  50  c.c.  mark,  and  to  each  is 
added  i  c.c.  dilute  sulphuric  acid,  and  i  c.c. 
meta-phenylene-diamine.  They  are  allowed  to 
stand  at  least  twenty  minutes,  and  the  colours  are 
then  compared  as  in  Nesslerising. 

"  Example  : — 

50  c.c.  sewage  effluent  =  5  c.c.  standard  sodium 

nitrite. 

=  0*05  mgm.  nitrogen. 
=  0*07  grain  nitrogen  per  gallon." 

F  2 


68         SEWAGE   WORKS   ANALYSES. 


THE   DETERMINATION   OF   NITRATES. 

When  a  solution  containing  nitrate  or  nitrite  is 
subjected  to  the  action  of  a  reducing  agent,  such 
as  nascent  hydrogen,  it  is  converted   in   various 
stages,  involving  the  formation  of  nitrous  acid  and 
hydroxylamine,  finally  into  ammonia,  thus : — 
HNO3+H2=HNO2+H2O 
HNO2-f-2H2=H2NOH4-H2O 
NH2OH  +  H2=NH3+H2O. 

The  nitrogen  present  as  nitrate  can  thus  be 
determined  by  reducing  to  ammonia  and  estimating 
the  ammonia  by  Nesslerisation.  This  method  has 
been  found  in  practice  to  be  simple,  at  the  same 
time  giving  very  accurate  results. 

It  is  obvious,  however,  that  any  nitrite  present 
will  also  be  reduced;  the  nitrogen  combined  as 
nitrite  must  therefore  be  separately  estimated  and 
deducted  from  the  nitrogen  as  nitrate. 

The  most  satisfactory  method  of  reducing  nitrates 
has  been  found  to  be  by  means  of  the  copper  zinc 
couple. 

This  is  prepared  as  follows  : — 

A  piece  of  zinc  foil  about  six  inches  long  by  two 
inches  wide  is  rolled  into  a  cylinder  about  half 
an  inch  in  diameter,  then  dipped  for  a  moment  into 
strong  hydrochloric  acid,  to  clean  the  surface  of 
the  metal,  and  afterwards  well  washed  in  water. 
The  clean  cylinder  is  now  transferred  for  a  few 
moments  to  a  three  per  cent,  solution  of  copper 
sulphate  until  evenly  coated  with  a  black  layer 


SEWAGE   WORKS  ANALYSES.         69 

of  copper.  It  is  then  again  washed  by  gently 
immersing  in  clean  water  so  as  not  to  dislodge  the 
film  of  copper. 

Before  bringing  the  solution  into  contact  with 
the  couple,  it  is  advisable  to  drive  off  any  free 
ammonia,  as  otherwise  the  total  amount  of 
ammonia  to  be  determined  by  Nesslerisation  is 
inconveniently  large,  and  the  free  ammonia  must 
be  deducted  from  the  total  ammonia  present  after 
reduction. 

Any  error  in  the  determination  of  free  ammonia 
will  therefore  affect  the  nitrate  determination. 

The  free  ammonia  is  most  conveniently  driven 
off  with  steam  in  the  apparatus  described  on 
p.  58,  in  connection  with  the  method  for  deter- 
mining organic  ammonia.  In  this  way  the  addition 
of  large  quantities  of  water,  which  may  contain 
nitrates  and  cause  the  experimental  correction  to 
be  too  high,  is  avoided.  As  the  ammonia  is  dis- 
solved in  the  condensed  distillate,  there  is  also  no 
risk  of  its  escape  into  the  laboratory  to  interfere 
with  the  Nessler  test. 

Seventy  c.c.  of  the  sample  are  taken  and  distilled 
with  steam  till  no  free  ammonia  can  be  detected 
in  the  distillate  on  Nesslerisation. 

The  residual  solution  from  which  the  free 
ammonia  has  been  expelled  is  now  poured  into 
a  glass  cylinder  six  inches  high  by  one  inch  in 
diameter  and  the  zinc  copper  couple,  prepared  as 
above,  added.  Thorough  contact  of  the  couple 
and  the  solution  is  thus  ensured. 


70         SEWAGE   WORKS  ANALYSES. 

On  slightly  acidifying  the  solution  with  acetic 
acid  (i  acid:  2  water),  an  evolution  of  hydrogen 
occurs  which  reduces  the  nitrate  to  ammonia. 
For  the  reaction  to  be  complete  it  should  be  left 
over  night,  and  for  further  precaution  a  known 
amount  of  the  solution  may  be  tested  for  nitrites 
in  the  morning.  If  these  are  present,  it  is  evident 
that  the  reduction  to  ammonia  is  incomplete  and 
must  be  further  continued.  This  is,  however, 
seldom,  if  ever,  necessary. 

If  reduction  is  complete,  the  solution  is  poured 
off  from  the  copper  zinc  couple  into  a  litre 
capacity  flask,  the  couple  is  washed  free  from 
adhering  liquid  and  the  washings  are  added  to 
the  flask. 

Any  free  acid  still  remaining  must  be  neutralised 
with  a  little  powdered  sodium  carbonate;  tap- 
water  is  then  added  to  make  up  the  volume  to 
about  500  c.c.,  and  the  ammonia  distilled  off  and 
estimated  as  on  p.  52. 

From  time  to  time  a  blank  experiment  should 
be  made,  the  whole  process  being  conducted  as 
above,  with  the  exception  that  distilled  water  is 
substituted  for  the  sample. 

Any  ammonia  found  in  the  blank  experiment 
must  be  deducted  from  the  total  amount  obtained 
from  the  sample. 

The  following  is  Mr.  Scudder's  description 
of  the  method  used  in  the  Mersey  and  Irwell 
Joint  Committee's  laboratory.  It  is  useful  where 
results  are  required  to  be  obtained  in  one  day; 


SEWAGE   WORKS  ANALYSES.         71 

the  method  above  described,  however,  requires  no 
greater  amount  of  actual  manipulation,  and  has 
been  found  to  work  in  well  with  the  daily  routine. 
The  results  given  are  also  exceedingly  trustworthy. 
The  caustic  soda  used  for  neutralisation,  as  in 
the  method  described  by  Mr.  Scudder  (seq.)  may 
if  added  in  excess  in  certain  cases  liberate  a  little 
ammonia  from  albuminoids  and  cause  the  nitrate 
determination  to  be  somewhat  high. 

"  ESTIMATION   OF   NITRIC   NITROGEN. 

"  Seventy  c.c.  of  the  sewage  effluent  are  placed 
in  a  nickel  basin,  0-5  c.c.  normal  carbonate  of  soda 
solution  added,  and  evaporated  to  dryness  on  a 
water  bath  to  remove  free  and  saline  ammonia. 
The  residue  is  dissolved  in  distilled  water  and 
transferred  to  a  6  by  i \  inch  preparation  tube  with 
mark  scratched  at  50  c.c. 

"  The  liquid  is  made  up  to  the  mark  with  distilled 
water;  5  c.c.  of  25  per  cent,  pure  hydrochloric 
acid  (distilled  from  H2SO4  to  render  NH3  free)  is 
added.  Next  add  a  piece  of  thin  aluminium  sheet, 
weighing  from  0*5  to  0*7  grm.,  and  measuring  about 
two  inches  by  one  inch,  which  has  been  amal- 
gamated either  by  dipping  it  into  mercuric  chloride 
solution  or,  preferably,  by  standing  twenty  minutes 
in  Nessler  residues  and  then  washing  with  distilled 
water.  A  vigorous  action  at  once  commences, 
the  nascent  hydrogen  reducing  the  nitric  nitrogen 
to  ammonia,  and  to  prevent  escape  of  vapour 


SEWAGE  WORKS  ANALYSES. 


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SEWAGE   WORKS   ANALYSES.         73 

a  cork,  fitted  with  S -shaped  protection  tube,  filled 
with  glass  wool  moistened  with  water,  is  inserted. 
No  ammonia  can  escape,  as  it  is  held  by  the  acid 
solution.  In  this  manner  one  grain  nitrogen  as 
nitrites  and  nitrates  per  gallon  can  easily  be  re- 
duced to  ammonia  in  one  hour.  After  reduction 
the  acid  solution  is  just  neutralised  with  caustic 
soda  liquid  (which  has  been  boiled  free  from 
ammonia)  in  a  flask  and  distilled.  The  ammonia 
in  the  distillate  is  then  determined  by  Nessler 
solution,  exactly  in  the  same  manner  as  a  free 
ammonia  estimation.  From  the  amount  of 
ammonia  found,  the  quantity  of  nitric  nitrogen  is 
calculated  in  the  usual  way,  viz.,  by  multiplying 
the  amount  found  per  gallon  of  effluent  by  0*82." 

The  examples,  on  the  opposite  page,  determined 
in  working  the  bacterial  contact  beds  in  Man- 
chester, will  illustrate  the  application  of  the  results 
obtained  by  the  foregoing  methods,  and  also  the 
different  systems  of  recording  the  analytical  figures 
(see  p.  17). 

The  quantity  of  sewage  or  tank  effluent  which 
can  be  safely  put  upon  a  continuous  filter  can  be 
controlled  by  similar  observations. 

It  may  be  here  noted  that  the  activity  of  the 
nitrification  process  should  properly  be  estimated 
by  the  amount  of  nitrogen  in  the  liquid  passing 
on  to  the  filter,  which  is  recovered  as  nitrate 
in  the  filtered  effluent.  Such  a  comparison  can 
only  be  made  from  continuous  observations  ex- 
tending over  a  prolonged  period.  Isolated  analyses 


74 


SEWAGE   WORKS  ANALYSES. 


do  not  sufficiently  allow  for  the  effect  of  periods 
of  rest. 

The  following  numbers  are  the  average  results 
obtained  from  the  experimental  contact  beds  in 
Manchester  during  a  period  of  three  months. 


Grains  per  Gallon. 

Description  of  Sample. 

Albumi- 

Ammonia 

Ammonia. 

noid 
Ammonia. 

from 

Nitrates. 

Open  septic  tank  effluent 
Bacteria    bed     effluent    (first 

I-Q4 

*34 

Nil. 

contact)           

77 

•10 

75 

Bacteria  bed   effluent  (second 

contact)          

•26 

•04 

•98 

From  the  above  figures  it  will  be  seen  that  of 
the  total  ammonia  found  in  the  tank  effluent — 
i.e.,  2*28  grains  per  gallon — '75  grains,  or  about 
33  per  cent.,  has  been  converted  into  nitrate  in 
the  first  contact  bed ;  and  this  is  increased  to 
•98  grain,  or  about  43  per  cent.,  in  the  second 
contact  bed.* 

A  considerable  percentage  of  ammonia  is  un- 
accounted for  in  the  above  figures,  and  doubtless 
has  escaped  as  nitrogen  in  consequence  of  denitri- 
fication  changes,  such  as  are  described  on  p.  62. 

*  The  second  contact  bed  in  this  instance  was  worked  at 
twice  the  rate  of  the  primary  bed. 


SEWAGE  WORKS   ANALYSES.         75 


CHAPTER   V. 

THE   DETERMINATION   OF   DISSOLVED 
OXYGEN. 

THE  determination  of  dissolved  oxygen  in  an 
effluent,  or  in  the  stream  into  which  it  flows, 
is  of  importance  as  showing  the  reserve  of  this 
element  available  for  further  purification. 

It  is  also  of  importance  to  determine  the  rate  at 
which  an  effluent  will  take  up  oxygen  from  fully 
aerated  water.  This  indicates  clearly  the  effect 
which  such  an  effluent  will  have  upon  a  stream. 

A  very  satisfactory  method  for  the  determination 
of  dissolved  oxygen  is  that  of  Dr.  Thresh.* 

This  depends  on  the  liberation  of  nitric  oxide 
(NO)  in  the  solution  to  be  tested,  which  com- 
bines with  the  dissolved  oxygen  to  form  nitrogen 
trioxide  (N2O3).  The  NO  is  liberated  by  the 
interaction  of  sodium  nitrite,  potassium  iodide, 
and  sulphuric  acid.  The  N2Os  formed  liberates 
free  iodine  from  the  potassium  iodide  present, 
equivalent  to  the  oxygen  in  solution.  This  iodine 
can  be  determined  by  addition  of  sodium  thio- 
sulphate  solution. 

*  "  Journ.  Chem.  Soc.,"  1890,  p.  185. 


76         SEWAGE   WORKS   ANALYSES. 

The  various  reactions  are  expressed  by  the 
following  equations  :  — 

The  potassium  iodide,  sodium  nitrite,  and 
sulphuric  acid  react  to  form  free  I  and  N  O. 

2KI-fH2SO4  =  K2SCV 


+  2HNO2 

The  nitric  oxide  liberated  combines  with  the 
oxygen  in  the  water  to  form  N2O3  thus  :  — 
2NO  +  O=N203. 

In  contact  with  the  hydriodic  acid  a  further 
quantity  of  iodine  is  liberated  equivalent  to  the 
oxygen  present,  thus:  — 


The  total  iodine  liberated  reacts  with  the  sodium 
thiosulphate  added,  thus  (sodium  tetrathionate  and 
sodium  iodide  being  formed)  :  — 

Na2S2O3+  12==  Na2S4O6+  2NaI. 

If  the  iodine  liberated  in  the  initial  reaction  is 
separately  determined,  the  remainder  of  the  iodine 
is  equivalent  to  the  oxygen  present. 

The  following  solutions  are  necessary  for  carry- 
ing out  the  determination  :  — 

(i.)  '5  grm.  sodium  nitrite  and  20  grm.  potassium 
iodide  are  dissolved  in  100  c.c.  of  water. 

(2.)  Sulphuric  Acid.  —  This  is  made  up  in  the  pro- 
portion of  i  acid  to  3  water,  with  the  precautions 
given  on  p.  24. 

(3.)  Starch  Solution.  —  Made  up  as  on  p.  24. 

(4.)  Standard  Sodium  Thiosulphate  Solution.  —  This 


FIG.  6.— THRESH  APPARATUS   FOR 
DETERMINING   DISSOLVED   OXYGEN. 


\_Tof ace  page  >tf. 


SEWAGE   WORKS  ANALYSES.         77 

should  be  made  of  such  a  strength  that  i  c.c.= 
•25  mgm.  oxygen.  For  this  purpose  rather  more 
than  775  grm.  are  dissolved  in  i  litre  of  water, 
and  the  solution  is  then  titrated  against  an  amount 
of  iodine  liberated  from  acidified  potassium  iodide 
by  25  c.c.  of  the  standard  permanganate  used  for 
determining  oxygen  absorption  (see  p.  23).  The 
25  c.c.  of  permanganate  should  be  equivalent  to 
10  c.c.  of  the  thiosulphate.  If  the  solution  of  the 
latter  is  too  strong — i.e.,  if  say  9  c.c.  are  equivalent 
to  25  c.c.  of  the  permanganate — then  water  must 
be  added  in  the  proportion  of  i  c.c.  to  every  9;  i.e.f 

1000  — q  r 

z=no  c.c.  of  water  is  to  be  added  to  the 

991  c.c.  remaining  after  titration. 

The  apparatus  used  is  shown  in  Fig.  6.  A  is  a 
bottle  capable  of  holding  about  500  c.c.  This  bottle 
is  closed  by  an  indiarubber  stopper  with  four  holes. 
Through  one  is  inserted  a  tap  cylinder  B  holding 
300  c.c. ;  through  another  passes  a  piece  of  glass 
tubing  to  which  is  attached  the  end  of  the 
burette  C  by  a  piece  of  indiarubber  tubing 
which  is  closed  by  a  pinch-cock.  The  remaining 
two  serve  for  the  inlet  and  outlet  of  a  supply  of 
coal-gas,  which  can  be  passed  into  B  as  required 
through  a  well  fitting  indiarubber  stopper  D,  any 
excess  being  burnt  at  E. 

Before  describing  the  analytical  process,  it  is  im- 
portant to  draw  attention  to  the  method  of  taking 
samples  for  determination  of  dissolved  oxygen. 

Such  samples  should  always  be  drawn  from  a 


78         SEWAGE  WORKS  ANALYSES. 

still  pool  of  the  liquid,  with  every  precaution  to 
avoid  splashing  or  exposure  of  a  large  surface  to 
the  air. 

This  is  best  accomplished  by  syphoning  the 
liquid  into  the  bottle.  For  this  purpose  the 
sample  bottle  is  provided  with  a  double-bored 
stopper,  through  one  hole  of  which  the  syphon 
tube  passes  to  the  bottom  of  the  bottle,  through 
the  other  a  tube  for  sucking  out  the  air.  By 
immersing  the  bottle  and  the  end  of  the  syphon 
under  the  liquid  and  drawing  out  the  air,  the 
liquid  rushes  in  and  fills  the  bottle  with  the 
minimum  absorption  of  oxygen.  By  connecting 
a  second  bottle  with  the  first,  and  filling  both 
bottles  with  the  water  as  before,  the  water  in  the 
first  bottle  can  be  collected  without  coming  into 
contact  with  air  at  all.* 

Having  thus  obtained  the  required  sample,  the 
oxygen  dissolved  in  the  liquid  is  determined  as 
follows : — 

The  sample  is  carefully  poured,  or  better, 
syphoned,  into  the  cylinder  B  until  this  is  filled 
to  the  neck  of  the  stopper ;  i  c.c.  of  the  nitrite- 
iodide  solution  is  added,  together  with  i  c.c.  of 
sulphuric  acid. 

The  solutions,  being  heavy,  flow  to  the  bottom 
of  the  cylinder;  the  stopper  D  is  now  inserted, 
and  the  whole  apparatus  inclined  once  or  twice  in 
order  to  mix  the  reagents  in  B.  The  reaction 
above  described  then  takes  place,  fifteen  minutes 
*  Letts'  "  Sanitary  Record,"  1901,  p.  423. 


SEWAGE   WORKS  ANALYSES.         79 

being  allowed  for  complete  diffusion.  During  this 
time  the  air  in  A  is  displaced  by  coal-gas,  which 
(after  allowing  time  for  the  air  to  be  driven  out  of 
A)  can  be  burnt  at  E. 

The  solution  in  B,  when  reaction  is  complete, 
is  allowed  to  flow  into  A  by  opening  the  tap 
of  B ;  the  liberated  iodine  is  then  titrated  against 
sodium  thiosulphate  run  in  from  C,  2  c.c.  of  starch 
being  added  through  the  tap  of  B  for  exactly 
determining  the  end  reaction. 

The  total  iodine  thus  determined  is  derived 
from  three  sources : — 

(a)  The  oxygen  dissolved  in  the  sample  used. 

(b)  The  oxygen  dissolved  in  the  reagents. 

(c)  The  nitrous  acid  from  the  nitrites. 

(d)  The  nitrous  acid  which  may  be  present  as 

nitrite  in  the  sample. 

The  iodine  due  to  (b)  and  (c)  is  determined  by 
adding  through  the  tap  of  B,  2  c.c.  of  the  nitrite 
iodide  solution,  2  c.c.  acid,  and  4  c.c.  starch,  and 
distilled  water  equal  to  twice  the  volume  of  thio- 
sulphate used  in  the  analysis,  and  titrating  as  in 
the  actual  experiment.  Half  the  oxygen  value  thus 
obtained  represents  the  amount  due  to  (b)  and  (c). 

If  a  series  of  determinations  have  to  be  made, 
the  oxygen  dissolved  in  the  thiosulphate  solution 
should  be  separately  estimated.  For  this  purpose, 
a  known  amount,  say  20  c.c.  of  distilled  water, 
may  be  taken,  and  the  dissolved  oxygen  contained 
in  it  determined ;  ^th  of  the  amount  found  may 
then  be  assumed  to  represent  the  dissolved  oxygen 


8o         SEWAGE   WORKS  ANALYSES. 

in  i  c.c.  of  the  thiosulphate.  A  correction  can 
then  easily  be  made  in  each  experiment  according 
to  the  amount  of  thiosulphate  used. 

To  obtain  the  correction  due  to  (d),  the  amount 
of  nitrite  expressed  in  terms  of  ammonia  present 
in  the  sample  may  be  determined  by  the  methods 
given  on  pp.  62  and  67.  The  oxygen  equivalent 
required  will  be  ^f  ths  of  this  ammonia  value. 

The  oxygen  dissolved  in  the  sample  may  be 
calculated  as  follows : — 

a  =  weight  of  oxygen  in  milligrammes  per  litre. 

b  =  c.c.  thiosulphate  equivalent  to  oxygen  dis- 
solved in  the  reagents. 

c  =  c.c.  thiosulphate  equivalent  to  nitrous  acid 
from  nitrite  added. 

d  =  c.c.  thiosulphate  equivalent  to  nitrous  acid 
from  nitrite  in  sample. 

e  =  total  number  of  c.c.  of  thiosulphate  used. 

/  =  capacity  of  B. 

Then  a  =  ~  (e  -  b  -  c  -  d)  x  -25 

(i  c.c.  thio.  =  '25  mgm.  O). 

If  the  volume  of  B  is  exactly  250  c.c.,  then 
a=(e-b-c-d). 

By  multiplying  the  results  thus  obtained  by 
•07  the  quantity  of  oxygen  present  in  grains  per 
gallon  is  ascertained. 

In  order  to  obtain  the  number  of  c.c.  of  oxygen 
per  litre,  the  number  of  milligrammes  per  litre 
should  be  divided  by  the  weight  of  i  c.c.  of 
oxygen,  viz.,  1*4336  mgm. 


SEWAGE   WORKS   ANALYSES.          81 

The  thiosulphate  solution  should  be  kept  in  the 
dark  to  avoid  changes  in  composition  due  to  the 
action  of  light,  and  should  be  restandardised  from 
time  to  time. 

The  method  employed  by  Mr.  Scudder  for 
determining  dissolved  oxygen  is  that  of  Roscoe 
and  Lunt.*  The  method  is  briefly  as  follows  : — 

A  solution  of  indigo  is  exactly  decolourised  by  a 
standard  solution  of  sodium  hyposulphite.  The 
indigo  is  re-oxidised  by  addition  of  the  sample 
containing  dissolved  oxygen,  and  the  amount  of 
oxidised  indigo  and  consequently  of  dissolved 
oxygen,  determined  by  titration  with  the  standard 
hyposulphite. 

The  process  as  originally  described  requires 
considerable  time  and  trouble  in  setting  up  the 
apparatus  in  the  first  instance,  although  the 
actual  method  of  analysis  is  simple.  A  portable 
modification  of  the  apparatus  has,  however,  been 
devised  by  Mr.  Scudder  suitable  for  making  analyses 
of  river  water,  etc.,  on  the  spot.  Other  improve- 
ments in  this  method  have  been  described  by 
Dr.  Gerland.t 

Another  method  for  rapidly  making  determina- 
tions with  a  fair  degree  of  accuracy  has  been 
recently  described  by  Prof.  Ramsay.  I  This 

*  "  Journ.  Chem.  Soc.,"  vol.  lv.,  1889,  p.  553.  See  also 
Sutton,  "  Volumetric  Analysis,"  pp.  297 — 304. 

t  "Journal  Society  of  Chemical  Industry,"  vol.  xv.,  1896, 
P- 15- 

|  "  Journal  Society  of  Chemical  Industry,"  vol.  xx.,  1901, 
p.  1071. 

S.W.  G 


82         SEWAGE   WORKS   ANALYSES. 

depends  on  the  measurement  of  the  blue  tint 
produced  when  the  sample  containing  dissolved 
oxygen  is  added  to  a  solution  of  ammoniacal 
cuprous  chloride. 

To  determine  the  rate  of  absorption  of  dissolved 
oxygen  by  a  sample  of  sewage  or  effluent,  a 
number  of  bottles  should  be  completely  filled 
with  equal  volumes  of  the  sample  and  of  tap- 
water  which  has  been  well  shaken  with  air. 
These  may  be  left  with  the  stoppers  inserted  for 
any  desired  time,  and  at  intervals  the  dissolved 
oxygen  in  the  mixture  determined. 

A  curve  may  then  be  plotted  of  the  amount  of 
oxygen  left  in  the  mixture  after  different  periods 
of  standing. 

Very  valuable  information  can  thus  be  obtained 
as  to  the  readiness  with  which  an  effluent  will  rob 
a  stream  of  dissolved  oxygen,  or,  in  other  words, 
of  the  amount  of  oxygen  in  solution  which  must 
be  presented  to  the  sample  in  order  to  prevent 
putrefaction  (see  Table,  p.  83). 

If  similar  experiments  be  conducted  in  open 
shallow  vessels,  the  rate  of  disappearance  of  dis- 
solved oxygen  will  be  much  slower,  or  complete 
absorption  of  the  oxygen  may  not  take  place  at 
all.  As,  however,  it  often  happens  that  only  the 
upper  stratum  of  the  stream  comes  much  in 
contact  with  the  air,  e.g.,  in  a  canal  or  sluggish 
river,  a  good  effluent  should  be  required  in  most 
cases  to  withstand  the  test  in  a  closed  bottle. 

The   method    employed    by   Mr.    Scudder   for 


SEWAGE  WORKS  ANALYSES. 


such   a    determination    is  described    by  him  as 
follows : — 

"Dissolved  Oxygen  Test. — 100  c.c.  of  the  sewage 
effluent  are  added  to  900  c.c.  fresh  water  (tap- 
water  is  used  in  my  laboratory)  in  a  half  Win- 
chester quart  bottle,  and  shaken  up  to  mix,  then 


Description  of  Sample. 

Time  standing  at 
Temperature  of  Labo- 
ratory before  Analysis. 

Dissolved  Oxygen. 
Grains  per  Gallon. 

Mixture  of  tank  effluent 

Nil. 

•478 

from   chemical    pre- 

2 hours 

•408 

cipitation  with  equal 

4  hours 

•327 

volume  of  aerated 

24  hours 

Nil. 

tap  -water. 

Mixture  of  open  septic 

Nil. 

•366 

tank     effluent    with 

i  hour 

'3°7 

equal  volume  of 

2  hours 

•245 

aerated  tap-water. 

3  hours 

•171 

4  hours 

•105 

5  hours 

•113 

6  hours 

•040 

Mixture  of  effluent  from 

Nil. 

*439 

second    contact  bed 

2  hours 

'436 

with  equal  volume  of 

4  hours 

m. 

*436 

aerated  tap  -water. 

24  hours 

'397 

48  hours 

•358 

allowed  to  stand  at  least  half  an  hour  to  allow 
small  air  bubbles  to  rise  to  the  surface.  The  dis- 
solved oxygen  in  the  diluted  effluent  is  determined. 
"Two  lo-oz.  stoppered  bottles  are  filled  with  the 
dihited  effluent  and  placed  in  the  incubator  at  a 

G  2 


84         SEWAGE   WORKS   ANALYSES. 

temperature  of  75°  Fahr.  After  standing  twenty- 
four  hours  one  of  the  bottles  is  taken  out  and  the 
dissolved  oxygen  in  it  determined.  After  forty- 
eight  hours  the  other  bottle  is  taken  out  and  the 
dissolved  oxygen  estimated. 

"  It  was  found  that  owing  to  the  pressure  some 
of  the  stoppered  bottles  cracked  round  the  bottom. 
In  order  to  avoid  this,  the  plan  now  adopted  is  to 
fit  to  the  bottle  an  indiarubber  stopper  containing 
a  piece  of  very  narrow  glass  tubing,  bent  to  S 
shape,  to  allow  for  expansion  of  the  liquid. 
Equally  accurate  results  are  obtained  with  this 
modification." 

Another  device,  with  the  same  object,  is  to 
provide  the  bottle  with  an  indiarubber  stopper 
containing  a  piece  of  narrow  glass  tubing  closed 
at  the  upper  end  by  a  small  piece  of  glass  rod 
joined  to  the  tube  by  close-fitting  indiarubber 
tubing.  A  certain  amount  of  expansion  is  thus 
permitted  by  the  indiarubber. 

The  results  are  expressed  in  grains  of  dissolved 
oxygen  absorbed  per  gallon  of  sewage  effluent. 

The  following  numbers  were  obtained  on  incu- 
bating mixtures  in  equal  proportions  of  ship  canal 
water  and  effluent  from  a  second  contact  bed,  for 
six  days  at  80°  F.  (26°  C.).  They  illustrate 
the  fact  that  in  presence  of  oxfdisable  matter  the 
dissolved  oxygen  tends  to  disappear  sooner  than 
the  nitrate.  In  cases  where  the  ship  canal  was 
in  a  bad  condition,  the  nitrate  in  the  mixture  also 
wholly  or  for  the  most  part  disappears.  The 
results  are  expressed  in  grains  per  gallon. 


SEWAGE   WORKS   ANALYSES. 


Ammonia  from  Nitrites 
and  Nitrates. 

Dissolved  Oxygen. 

Putrescibility. 

Before 
Incubator. 

After 
Incu- 
bator. 

Before 
Incubator. 

After 
Incu- 
bator. 

After  Incubator. 

Effluent  from 
second  contact 
bed. 

Ship  Canal 
water. 

Mixture. 

Effluent  from 
second  contact 
bed. 

Ship  Canal 
water. 

H 
§ 

Effluent  from 
second  contact 
bed. 

Ship  Canal 
water. 

Mixture. 

•56 

•19 

•48 

'54 

•60 

Nil. 

+ 

+ 

+ 

•85 

•13 

•38 

'Si 

•26 

Nil. 

+ 

— 

+ 

'55 

•17 

•30 

•40 

'14 

Nil. 

-f 

X 

+ 

•80 

'02 

Nil. 

•27 

•23 

Nil. 

+ 

— 

— 

Finally,  it  will  be  of  interest  to  include  some 
results  obtained  by  incubating  various  samples 
with  nine  volumes  of  aerated  tap-water  for  two 
days  at  80°  Fahr. 


Dissolved  Oxygen. 
Grains  per  Gallon. 

Sample. 

After 

At  Once. 

2  Days  in 

Incubator. 

Tank  effluent  from  chemical 

precipitation          

•699 

Nil. 

Effluent  after  septic  tank  and 

one  contact  (£-acre  bed)  ... 
Effluent  after  septic  tank  and 

•717 

•414 

two  contacts          

•711 

•610 

86          SEWAGE  WORKS  ANALYSES. 


CHAPTER   VI. 

THE  DETERMINATION  OF  CHLORINE, 
ACIDITY  AND  ALKALINITY,  AND 
IRON  COMPOUNDS. 

DETERMINATION   OF   CHLORINE. 

THIS  determination  is  of  value  as  it  affords  a 
measure  of  ascertaining  whether  the  samples  taken 
before  and  after  a  purification  process  really 
represent  the  same  sewage. 

The  chlorine  is  present  in  domestic  sewage 
chiefly  in  combination  with  sodium,  as  sodium 
chloride  or  common  salt.  In  manufacturing  sewage 
it  may  also  occur  as  ferrous  chloride  (iron  pickle) 
in  the  waste  liquors  from  galvanising  works,  or  as 
salt  in  spent  dye  liquor.  Occasionally  in  snowy 
weather,  when  salt  is  used  on  the  streets,  the 
chlorine  number  in  the  sewage  is  abnormally 
high.  But  in  any  case  it  is  unaffected  by  ordinary 
sewage  purification  processes,  and  if  the  sample  of 
effluent  really  represents  the  same  sewage  that 
was  purified,  then  the  chlorine  number  should  be 
nearly,  if  not  quite,  identical  in  the  two  cases. 

The  chlorine  number  also  gives  a  very  good  idea 
of  the  actual  dilution  of  the  sewage,  as  it  decreases 
simply  in  proportion  to  the  dilution. 


SEWAGE   WORKS  ANALYSES.         87 

The  determination  of  chlorine  depends  on  the 
fact  that  silver  nitrate  precipitates  chlorine  from 
chlorides  in  solution  as  a  white  precipitate  of  silver 
chloride,  thus : — 

NaCl  +  AgNO8  =  AgCl+NaNO8. 

If  to  the  solution  containing  chlorides  a  few 
drops  of  potassium  chromate  solution  are  added, 
then  as  soon  as  all  the  chlorine  has  combined  with 
the  silver,  a  deep  brown  precipitate  of  silver  chro- 
mate is  formed.  The  formation  of  the  red  silver 
chromate  indicates,  therefore,  the  end  of  the 
reaction,  and  if  the  volume  of  the  sample  is  known, 
and  if  the  volume  and  strength  of  the  silver  solu- 
tion necessary  for  a  complete  precipitation  of  the 
chlorine  is  also  known,  then  the  amount  of  the 
latter  present  can  be  calculated. 

The  following  solutions  are  required  for  the 
determination. 

Standard  Silver  Nitrate  Solution. — 4*795  grms. 
pure  silver  nitrate  are  dissolved  in  one  litre  of  pure 
distilled  water.  No  turbidity  should  be  formed 
when  the  solution  is  made. 

Each  c.c.  of  this  solution  is  equivalent  to  one 
mgm.  chlorine. 

Potassium  Chromate  Solution. — Twenty  grms. 
recrystallised  potassium  chromate  are  dissolved 
in  200  c.c.  water. 

To  make  the  determination  35  c.c.  or  70  c.c.  of 
the  sample  are  taken,  according  to  dilution,  in  a 
white  porcelain  dish ;  2  c.c.  of  the  chromate  are 
added  and  the  silver  solution  added  from  a  burette 


88         SEWAGE   WORKS   ANALYSES. 

until,  after  stirring,  the  red  colour  of  the  silver 
chromate  is  just  apparent.  The  number  of  c.c. 
of  silver  solution  is  equal  to  the  number  of  mgms. 
of  chloride  in  the  quantity  of  sample  taken.  If 
less  or  more  than  70  c.c.  of  this  are  used  for  the 
determination,  the  quantity  present  in  70  c.c. 
(i.e.,  the  number  of  grains  in  a  gallon)  must  be 
calculated.  For  example  : — 

Thirty-five  c.c.  of  the  sample  required  7'2  c.c.  of 
the  standard  silver  nitrate  solution  before  a  per- 
manent red  precipitate  of  silver  chromate  was 
produced. 

The  sample  therefore  contains  7*2  x  2  mgms. 
chloride  in  70  c.c. — i.e.,  14*4  grains  chlorine  per 
gallon. 

If  the  liquid  to  be  tested  is  acid  (e.g.,  from  the 
presence  of  iron  pickle)  a  drop  or  two  of  ammonia 
should  be  added  to  the  measured  solution  which  is 
then  boiled  till  neutral,  or  pure  caustic  soda  (free 
from  chloride)  added  very  carefully  till  the  solution 
is  exactly  neutral.  If  the  sample  contains  much 
suspended  matter,  this  should  be  filtered  off,  the 
paper  being  moistened  only  with  the  sample,  and 
the  chlorine  determined  in  a  known  volume  of  the 
filtrate.  Some  slight  source  of  error  is  to  be 
found  in  the  presence,  especially  in  septic  tank 
effluent,  of  sulphides  in  solution,  which  cause  a 
precipitation  of  silver  sulphide  and  thus  give 
slightly  higher  results.  Such  differences  are, 
however,  seldom  large  enough  to  seriously  affect 
the  results.  The  slight  diminution  in  the  chlorine 


SEWAGE   WORKS   ANALYSES.         89 

figure  which  is  noted  after  septic  tank  effluent  has 
been  treated  in  bacterial  filters  is  no  doubt  partly 
due  to  this  cause. 

In  the  case  of  Manchester  sewage,  sulphocya- 
nates  are  present  in  the  waste  liquor  from  ammonia 
recovery  processes.  These  are  precipitated  by 
AgNOa  m  a  similar  manner  to  chlorides,  but  as 
they  are  oxidised  in  bacterial  filters  there  is  an 
apparent  loss  of  chlorine  in  the  filtrate,  due  really 
to  oxidation  and  disappearance  of  the  sulphocya- 
nates  in  the  tank  effluent. 

The  following  examples  will  serve  to  show  the 
relation  between  the  chlorine  figures  in  sewage 
which  has  passed  through  various  purification 
processes,  or  which  has  been  diluted  by  rain  : — 

Chlorine 
(Grains  per  Gallon). 

Sewage in 

Effluent  after  chemical  treatment  ...  iro 

Open  septic  tank  effluent.       ...  ...  11*4* 

Filtrate  from  first  contact  bed  ...  10*9* 

Filtrate  from  second  contact  bed  ...  10-5* 

First  flush  of  storm  water      ...  ...       9*6 

Storm  water      ...         ...         ..,  ...       3*8 

DETERMINATION   OF  ACIDITY  AND   ALKALINITY. 

It  has  been  already  explained  (Chap.  III.)  that 
ordinary  sewage  invariably  contains  ammonium 
carbonate  arising  from  the  decomposition  of  urea. 

*  These  figures  show  the  slight  decrease  in  the  chlorine 
number,  due  to  oxidation  of  sulphides  and  sulphocyanates  in 
the  Manchester  septic  tank  effluent,  by  the  bacterial  filters. 


go         SEWAGE   WORKS   ANALYSES. 

It  will  also  contain  in  solution  free  carbonic  acid, 
either  from  incipient  decomposition  of  carbona- 
ceous matter  or  from  the  decomposition  of 
ammonium  carbonate,  by  mineral  acids  sent  into 
the  sewers  from  manufacturing  processes.  These 
will  also  liberate  fatty  acids  from  the  soap  present 
in  the  sewage.  The  sewage  as  it  enters  the 
works  may  also  sometimes  contain  free  alkali,  e.g., 
chloride  of  lime ;  or  free  mineral  acid,  e.g.,  hydro- 
chloric acid  from  iron  pickling  waste,  or  sulphuric 
acid  from  benzol  washings. 

The  changes  taking  place  in  the  septic  tank 
result  in  the  formation  of  carbonic  acid  and  also 
of  sulphuretted  hydrogen,  both  of  which  gases 
dissolve  in  the  effluent  and  give  it  a  weakly  acid 
reaction  when  tested  with  a  reagent  known  as 
phenol-phthalein. 

The  determination  of  the  alkalinity  or  acidity  of 
a  sewage  from  time  to  time  is  essential  for  its 
proper  chemical  treatment.  It  affords  besides 
valuable  information  as  to  the  character  of  the 
liquid  entering  or  leaving  the  septic  tank  or  being 
put  upon  the  bacteria  beds. 

For  the  determination  of  acidity  and  alkalinity 
the  following  solutions  are  necessary : — 

Phenol-phthalein. — This  is  an  organic  compound  of 

the  formula  CO<^^XC6H4OH)8.    It  is  a  white 

solid,  formed  by  heating  together  phenol  and 
phthalic  anhydride.  It  has  the  property  of  form- 
ing crimson  compounds  with  alkalies,  which  are 


SEWAGE   WORKS   ANALYSES.          91 

decomposed  by  CO2,H2S,  and  organic  as  well 
as  mineral  acids.  Its  indications  are,  however, 
untrustworthy  in  presence  of  much  ammonia  or 
ammonium  salts. 

To  prepare  the  solution,  5  grms.  of  the  solid  sub- 
stance are  dissolved  in  i  litre  of  60  per  cent,  alcohol. 

Methyl-Orange  is  an  azo  dye  (para-dimethyl- 
aniline-azo-benzene-sulphonic  acid  CeH^SOaH) 
N2C6H4N(CH3)2);  it  gives  a  yellow  colour  with 
alkalies  and  alkaline  carbonates,  which  is  turned 
pink  in  presence  of  free  mineral  acid.  It  is  un- 
affected by  carbonic  acid  and  many  organic  acids. 

To  prepare  the  solution  i  grm.  of  the  solid 
substance  is  dissolved  in  i  litre  of  distilled  water. 

Solutions  of  the  above  indicators  are  generally 
supplied  ready  made  up. 

Standard  Sulphuric  Acid. — In  order  to  obtain  a 
normal  solution  of  sulphuric  acid,  50  grms.  of  the 
pure  acid  are  dissolved  carefully  in  a  litre  of 
water.  Several  grms.  of  purest  sodium  carbonate 
(Na2CO3)  are  carefully  heated  (best  in  a  platinum 
dish)  over  the  blow-pipe  flame  and  allowed  to  cool 
in  a  desiccator.*  One  grm.  of  this  dried  carbonate 
is  carefully  weighed  and  dissolved  in  distilled 
water,  and  a  few  drops  of  methyl  orange  added. 
The  standard  acid  is  run  in  from  a  burette  till  the 
solution  is  just  pink.  This  volume  of  acid  equals 
i  grm.  NaCO3.  It  is  well  to  check  this  deter- 

*  A  large  glass  bell-jar,  under  which  a  small  beaker  con- 
taining strong  sulphuric  acid,  or  calcium  chloride,  is  placed, 
makes  a  convenient  desiccator. 


92         SEWAGE   WORKS  ANALYSES. 

mination  by  a  second,  similarly  carried  out;  or 
I  grm.  Na2CO3  may  be  dissolved  in  250  c.c.  of 
water,  and  50  c.c.  of  this  solution  taken  for  titra- 
tion.  Three  or  four  titrations  may  thus  be  made, 
and  the  mean  value  multiplied  by  five  will  give  the 
volume  of  the  acid  equivalent  to  i  grm.  Na2CO8. 
The  volume  of  acid  is  then  calculated  which  is 
just  equivalent  to  half  the  molecular  weight  ex- 
pressed in  grms.  of  sodium  carbonate,  viz.,  53  grms., 
the  equation  being  as  follows  :  — 


If,  as  should  be  the  case,  this  quantity  is  rather 
less  than  a  litre  (the  acid  being  purposely  taken 
rather  strong),  then  such  quantity  of  distilled 
water  should  be  added  that  i  litre  of  the  acid  will 
contain  exactly  49  grms. 

Thus,  supposing  50  c.c.  of  the  sodium  carbonate 
solution  required  3*5  c.c.  of  the  acid  solution  for 
neutralisation,  then  i  grm.  Na2CO3  will  require 
3-5x5  =  16*5  c.c.  of  acid  ;  53  grms.  will  there- 
fore require  53  X  16*5  =  874*5  c.c.,  and  this  quantity 
of  acid  will  contain  49  grms.  HgSO*. 

The  quantity  of  acid  remaining  after  titration 
should  therefore  be  diluted  in  the  proportion  of 
874*5  c.c.  to  1000  c.c.,  or  874*5  c.c.  may  be  taken 
and  diluted  exactly  to  I  litre  with  distilled  water, 
and  the  rest  of  the  acid  rejected. 

One  c.c.  of  this  acid  now  contains  49  mgms. 
H2SO4.  *53  grm.  Na3  CO3  should  be  exactly 
neutralised  by  10  c.c.  of  the  acid. 


SEWAGE   WORKS   ANALYSES.         93 

The  standard  acid  thus  obtained  may  be  checked 
by  re-titrating  against  pure  sodium  carbonate. 

For  ordinary  use  a  decinormal  solution  should 
be  prepared  by  diluting  100  c.c.  of  the  above  acid 
to  i  litre. 

One  c.c.  of  the  above  acid  now  contains  4*9 
mgms.  H2SO4. 

Standard  Caustic  Soda. — This  may  be  prepared 
by  dissolving  between  20  and  30  grammes  metallic 
sodium  in  distilled  water.  The  sodium  should  be 
cut  to  a  clean  surface  before  weighing,  and  then 
cut  into  small  pieces,  which  are  carefully  added 
to  the  water  contained  in  a  shallow  earthenware, 
or  better,  silver  dish.  When  all  the  sodium  is 
dissolved  the  solution  is  made  up  to  i  litre,  and 
titrated  against  the  normal  acid  prepared  as  above 
described.  After  titration  the  soda  solution  must 

be  so  diluted  that  i  c.c.  =  i  c.c.  —  H2SO4. 

10 

Thus,  supposing  10  c.c.  of  the  acid  required 
7  c.c.  of  the  caustic  soda  solution  for  neutralisa- 
tion, then  for  every  7  c.c.  of  caustic  soda  solution 
left  after  titration  3  c.c.  of  distilled  water  must  be 
added. 

Distinction  must  be  drawn  between  what  may 
be  conveniently  termed  free  and  combined  alkalinity. 

Free  alkali  is  indicated  by  giving  a  crimson 
coloration  with  phenol-phthalein.  It  can  there- 
fore be  determined  by  adding  a  few  drops  of 
phenol-phthalein  and  then  standard  acid  from 
a  burette,  to  the  sample,  till  the  crimson  colour 


94         SEWAGE  WORKS  ANALYSES. 

disappears.  Free  alkali  is  seldom  present  in 
sewage,  except  occasionally  as  chloride  of  lime; 
but  if  lime  has  been  used  for  chemical  treatment, 
some  free  lime  should  be  present  in  the  effluent. 

The  results  given  when  phenol-phthalein  is  used 
as  an  indicator  must  only  be  considered  as  approxi- 
mate, as  its  action  is  influenced  by  the  presence  of 
ammonium  salts  and  by  variations  in  the  conditions 
of  working.  Moreover  the  presence  of  iron  com- 
pounds in  the  sewage  further  interferes  with  its 
accurate  use  as  an  indicator.  By  working  always 
in  the  same  manner,  however,  comparative  results 
may  be  obtained  which  will  show  any  marked 
changes  in  the  acidity  or  free  alkalinity  of  the 
sewage. 

It  is  important,  particularly  in  controlling  the 
addition  of  lime  to  the  sewage,  to  always  use  the 
same  strength  and  the  same  amount  of  phenol- 
phthalein. 

By  combined  alkalinity  is  meant  alkaline 
carbonates,  e.g.,  ammonium  carbonate. 

To  determine  combined  alkalinity  a  few  drops 
of  methyl  orange  are  added  to  a  measured  volume 
of  the  sample  and  standard  acid  added  until  the 
carbonate  is  decomposed,  i.e.,  until  the  methyl 
orange  is  turned  pink. 

Free  carbonic  acid  is  determined  by  adding 
phenol-phthalein  and  then  standard  alkali  till  a 
crimson  colour  is  obtained. 

Free  mineral  acid,  on  the  other  hand,  will  give 
a  pink  colour  with  methyl-orange,  and  standard 


SEWAGE   WORKS   ANALYSES.         95 

alkali  must  be  added  till  this  is  changed  to 
yellow. 

70  c.c.  are  usually  taken  for  the  estimation,  and 
the  sample  should  be  filtered,  if  necessary,  before 
the  standard  solution  is  added  from  a  burette. 

The  acidity  or  alkalinity  may  be  conveniently 
recorded  in  terms  of  the  number  of  c.c.  of  deci- 
normal  alkali  or  acid  required  per  70  c.c.,  or  from 
these  values  may  be  calculated  the  number  of 
grains  per  gallon  of  lime  as  CaO  equal  either  to 
the  acid  or  alkali  present. 

Examples : — 

Acidity. — Raw  sewage  containing  iron  pickle, 

"M 
70  c.c.  required  5*20  c.c.  — NaOH. 

N 
Acidity  =  5*2  in  terms  of  c.c.  —  NaOH  per  70  c.c. 

The  number  of  grains  CaO  to  which  this  is 
equivalent  per  gallon  is  calculated  as  follows  : — 

Each  c.c.  of  the  decinormal  soda  solution  is 
equivalent  to  half  the  molecular  weight  of  lime 
CaO  (expressed  in  milligrammes),  divided  by  10, 

i.e.    — 5          The  acidity  is  therefore  equivalent  to 
2  x  10 

5*2  x  2'8  =  15*36  grains  CaO  per  gallon. 
Lime  must  therefore  be  added  at  this  rate  in 
order  to  neutralise  the  acidity  of  the  sewage. 

DETERMINATION    OF    IRON. 

The  determination  of  the  amount  of  iron  present 
in  the  ferrous  or  ferric  state  is  of  importance  where 
iron  compounds  are  used  for  chemical  treatment, 


96         SEWAGE   WORKS   ANALYSES. 

or  where  iron  pickling  liquor  is  present  in  the 
sewage.  In  both  cases  iron  will  be  found  in  the 
effluent  after  chemical  treatment ;  but  if  sufficient 
lime  has  been  added  the  amount  present  is  only 
small.  An  excess  will  tend  to  separate  out  after- 
wards, either  as  oxide,  if  the  liquor  is  oxidised  in 
a  bacteria  bed,  or  as  sulphide,  if  it  should  be  under 
conditions  liable  to  set  up  putrefaction. 

Where  septic  treatment  is  in  force  the  iron 
pickle  will  enter  the  septic  tank  and  be  partially 
deposited  therein  as  sulphide.  The  amount  of 
iron  in  suspension,  and  solution  entering  and 
leaving  the  tank  is  of  importance  in  determining 
the  length  of  time  the  tank  should  run  without  at 
any  rate  partial  emptying ;  and  also  in  determining 
the  quantity  of  mineral  matter  passing  away  on  to 
the  bacterial  filters. 

FERROUS   IRON. 

The  determination  of  ferrous  iron  depends  upon 
the  depth  of  blue  coloration  produced  when 
potassium  ferricyanide  is  added  to  the  sample  in 
presence  of  acid.  The  solutions  required  are  : — 

Ferrous  ammonium  sulphate  ((NH^SO-jFeSO* 
6H2O). 

•35  gramme  of  this  salt  is  dissolved  in  500  c.c. 
distilled  water  —  i  c.c.  contains  'i  mgm.  iron. 
This  solution  rapidly  oxidises  and  should  be  made 
up  afresh  every  day. 

Potassium  Ferrocyanide. — Saturated  solution. 

Sulphuric  Acid. — One  part  acid  is  carefully  mixed 


SEWAGE   WORKS   ANALYSES.          97 

with  two  parts  water,  the  total  volume  of  the 
mixture  being  conveniently  about  one  litre. 

To  make  the  determination  a  number  of 
standards  are  made  up  from  the  standard  ferrous- 
ammonium  sulphate,  containing  varying  quantities 
of  iron  from  *i  mgm.  to  *5  mgm.  These  are 
contained  in  50-0. c.  Nessler  glasses,  10  c.c.  of 
sulphuric  acid  (one  part  acid  to  three  of  water) 
are  added,  and  then  potassium  ferricyanide,  until 
the  blue  colour  formed  attains  a  maximum ;  35  c.c. 
of  the  sample  are  taken  and  treated  similarly  to 
above,  and  the  depth  of  colour  noted  and  com- 
pared with  the  above  standards. 

Thus,  if  the  shade  is  between  the  standards 
'2  mgm.  and  "3  mgm.,  the  amount  is  taken  at 
•25  mgm.,  i.e.,  *5  in  70  c.c.  or  '5  grain  per  gallon. 

Instead  of  making  up  a  number  of  standards, 
the  same  method  may  be  adopted  as  is  used  for 
the  determination  of  small  quantities  of  ammonia 
and  nitrous  acid  (see  pp.  54  and  62).  A  graduated 
Nessler  or  reagent  tube  may  be  used  for  one 
standard  solution  containing  '5  mgm.  Fe,  and  the 
comparison  made  by  pouring  out  the  solution  until 
the  colour  is  brought  down  to  that  produced  by 
35  c.c.  of  the  sample  contained  in  a  glass  of  equal 
dimensions,  or  if  the  sample  contains  more  iron 
than  the  standard  it  may  be  reduced  in  the  same 
way. 

FERRIC    IRON. 

The  determination  of  ferric  iron  depends  upon 
the    depth    of    red    coloration    produced    when 
s.w.  H 


98          SEWAGE  WORKS  ANALYSES. 

potassium  sulphocyanate  is  added  to  the  sample 
in  presence  of  acid.  The  solutions  necessary  are 
the  following : — 

Iron  A  mmonium  A  turn. — 

((N  H4)2  S04  Fe  2(S04)324H2O) . 

1*8685  grms.  are  dissolved  in  i  litre  of  distilled 
water — 

I  c.c.  =  *i  mgm.  iron. 

Potassium  Sulphocyanate. — This  is  used  as  con- 
centrated as  possible. 

Sulphuric  Acid.  —  One  part  acid  to  two  parts 
water. 

The  determinations  are  carried  out  as  in  the 
case  of  ferrous  iron,  iron  alum  solution  being  used 
to  make  the  standard  solution,  and  potassium 
sulphocyanate  instead  of  potassium  ferricyanide 
to  produce  the  coloration. 

It  is  very  important  that  excess  of  sulphocyanate 
should  be  present  in  the  case  of  each  comparative 
test.  The  colour  increases  up  to  a  certain  constant 
limit  with  increase  of  sulphocyanate. 

It  is  important  that  iron  in  solution  should  be 
determined  as  soon  as  possible  after  collection  of 
the  sample,  as  it  tends  to  separate  out  on  standing. 
Thus  a  sample  of  sewage  which  gave  '36  grains 
per  gallon  Fe  in  solution  when  analysed  at  once, 
gave  only  '19  when  analysed  after  one  week's 
standing. 

IRON   IN   SUSPENSION. 

Where  much  of  the  iron  present  is  in  suspension 
in  the  liquid — for  example,  in  the  case  of  sewage  or 


SEWAGE   WORKS   ANALYSES.          99 

septic  tank  effluent  which  contains  some  propor- 
tion of  iron  pickle — the  most  accurate  method  of 
determining  the  iron  is  to  filter,  say,  140  c.c.  or 
more  through  a  Swedish  filter-paper,  wash  and 
burn  the  paper  and  residue,  and  fuse  the  dry 
mineral  matter  in  a  porcelain  or  platinum  crucible 
with  a  little  fusion  mixture  (equal  parts  of  sodium 
and  potassium  carbonate).  The  fused  mass  is 
extracted  with  dilute  hydrochloric  acid  and 
boiled  with  a  little  nitric  acid.  This  solution 
may  be  made  up  to  500  c.c.,  and  the  iron  in 
50  c.c.  of  this  determined  colorimetrically  as 
above. 

If  the  total  amount  of  iron  present  is  large,  the 
colorimetric  method  may  be  usefully  checked  by  a 
direct  volumetric  determination  of  the  total  iron 
in  suspension. 

For  this  purpose  the  solution  after  fusion  and 
extraction  with  acid  is  filtered  if  necessary,  and  a 
small  piece  of  pure  zinc  added  to  reduce  the  ferric 
iron  to  the  ferrous  state.  The  ferrous  solution 
can  then,  after  removal  of  the  zinc  and  addition 
of  a  crystal  or  two  of  manganous  sulphate,  be 
titrated  directly  against  standard  permanganate. 
With  small  quantities  of  iron  the  permanganate 
used  for  the  oxygen  absorption  tests  may  be 
employed.  It  is  added  carefully  to  the  solution 
till  a  permanent  pink  colour  is  obtained,  the 
manganous  sulphate  preventing  the  free  hydro- 
chloric acid  present  from  affecting  the  perman- 
ganate. 

H  2 


TOO        SEWAGE   WORKS   ANALYSES. 

10    c.c.   permanganate  =  i    mgm.   oxygen  =  7 
mgms.  Fe. 
Thus— 

2  FeO  +  O  =  Fe2O3, 
2(56  +  16)  +  16  =  (112  +  48). 


SEWAGE  WORKS  ANALYSES.         101 


CHAPTER    VII. 

THE   DETERMINATION   OF   SOLIDS   IN 
SOLUTION   AND   SUSPENSION. 

SOLIDS   IN    SOLUTION. 

THE  determination  of  the  total  solids  in  solution 
is  not  of  the  same  importance  as  the  various 
analytical  processes  hitherto  considered,  as  many 
of  the  substances  in  solution  are  quite  harmless 
from  the  point  of  view  of  the  purity  of  the  effluent 
and  are  uninfluenced  by  the  process  of  purification. 
Such,  for  example,  are  the  chlorides  normally 
present  in  sewage,  and  other  inorganic  salts,  such 
as  sodium  or  calcium  sulphates,  which  are  derived 
from  various  manufacturing  processes. 

Moreover  the  determination  of  the  total  solids 
in  solution  when  performed  in  the  usual  way  by 
evaporation  of  the  liquid  on  the  water-bath,  may 
give  erroneous  results  on  account  of  the  volatilisa- 
tion with  steam  of  such  substances  as  ammonium 
carbonate  and  certain  organic  compounds  present 
in  sewage. 

A  more  correct  determination  could  be  made  by 
evaporation  of  the  liquid  at  the  ordinary  tempera- 
ture in  vacuo,  but  even  this  method  is  liable  to 
error  in  a  less  degree. 


102        SEWAGE  WORKS  ANALYSES. 

As  a  comparative  determination  where  absolute 
accuracy  is  not  necessary,  it  is,  however,  not  without 
interest. 

The  determination  of  solids  in  solution  before 
and  after  any  purification  process  may  at  any  rate 
serve  to  show  whether  more  or  less  matter  is  pre- 
sent in  solution  after  the  process,  and  thus  help  to 
give  some  information  as  to  the  changes  going  on. 

It  has  been  found,  for  instance,  that  there  is 
less  matter  in  solution  in  the  effluent  from  the 
septic  tank  than  in  the  sewage  entering  it,  pointing 
to  a  conversion  of  some  of  the  matters  in  solution 
into  gases  or  readily  volatile  substances. 

For  the  purpose  of  such  estimations  a  convenient 
quantity,  generally  140  c.c.,  of  the  sample  after 
filtration  through  paper,  (moistened  only  with  the 
sample,)  is  evaporated  in  a  weighed  platinum  basin 
over  the  water-bath,  dried  at  100°  to  110°  C.  in  a 
drying  oven,  cooled  in  a  desiccator  and  weighed. 

The  increase  in  weight  of  the  basin  gives  the 
quantity  of  matter  in  solution. 

When  a  number  of  determinations  have  to  be 
made  the  greater  part  of  the  evaporation  may  be 
done  by  boiling  down  in  conical  flasks  and  trans- 
ferring the  concentrated  liquid  to  the  platinum 
dish  for  final  evaporation  to  dryness. 

Somewhat  different  values  will  be  obtained  if  the 
sample  is  filtered  through  porous  porcelain  or 
through  parchment  which  will  retain  certain 
colloidal  substances  present  more  or*  less  in  a 
state  of  emulsion. 


SEWAGE   WORKS  ANALYSES.         103 

SOLIDS   IN   SUSPENSION. 

Of  more  value  is  the  determination  of  the  total 
solids  in  suspension.  The  direct  determination  of 
the  amount  and  character  of  the  suspended  matters 
in  raw  sewage  is  rendered  difficult  by  the  fact  that 
much  of  this  is  of  such  a  character  that  it  escapes 
collection  when  the  ordinary  samples  are  taken. 
Heavy  sandy  detritus  and  floating  garbage  must 
therefore  be  separately  collected,  weighed  in  bulk, 
and  one  or  more  as  nearly  as  possible  average 
samples  taken  for  a  proximate  analysis. 

This  is  effected  by  drying  about  a  pound  of  the 
sample  in  a  large  basin  over  the  water-bath,  or  on 
an  iron  plate  over  a  small  flame  (care  being  taken 
to  avoid  charring).  Large  pieces  of  coal,  clinker, 
wood,  etc.,  may  be  picked  out  and  separately 
weighed.  The  finer  portions  can  then  be  sepa- 
rated by  sieving,  and  a  determination  of  the 
organic  and  volatile  constituents  made  by  igni- 
tion of  weighed  portions  of  the  residue  on 
each  of  the  sieves.  Most  of  the  clay  present 
will  pass  through  the  finest  of  the  sieves  used, 
and  may  be  separated  from  any  intermixed  sand 
by  washing. 

In  this  way  a  very  fair  estimate  can  be  obtained 
of  the  value  of  the  detritus  for  burning  in  a 
destructor,  or  for  use  as  a  manure. 

It  is  of  great  importance  to  know  the  amount  of 
solids  in  suspension  passing  away  from  sedimenta- 
tion tanks,  or  remaining  after  treatment  with 


io4        SEWAGE   WORKS  ANALYSES. 

chemicals,  or  in  the  septic  tank.  Such  a  deter- 
mination will  indicate  the  amount  of  matter  likely 
to  be  deposited  in  a  stream  or  on  the  surface  of 
bacterial  filter-beds.  If  a  corresponding  deter- 
mination is  made  of  the  solids  in  suspension  in  the 
sewage,  then  the  amount  of  matter  deposited  in 
the  tanks  by  a  given  volume  of  sewage  can  be 
calculated. 

The  further  determination  of  the  proportion  of 
mineral  as  compared  with  the  organic  and  volatile 
constituents  of  the  suspended  matter  indicates 
how  much  of  the  latter  is  possibly  resolvable  into 
gaseous  or  soluble  bodies  by  the  actions  taking 
place  in  the  septic  tanks,  in  the  bacterial  filters, 
or  in  the  stream  into  which  the  effluent  flows. 

The  most  accurate  method  of  carrying  out  such 
determinations  without  special  apparatus  is  to 
filter  a  known  volume  of  the  sample  through  a 
weighed  filter-paper,  wash,  dry  at  100°  to  110°  C 
and  weigh. 

The  mineral  matter  can  then  be  determined  by 
burning  the  filter-paper  in  a  weighed  crucible, 
heating  the  residue  to  redness,  moistening  with 
ammonium  carbonate,  to  convert  any  free  lime 
present  into  carbonate,  heating,  and  weighing, 
the  weight  of  residue  left  after  burning  off  the 
organic  matter  representing  non-volatile  mineral 
matter. 

The  filter-paper  used  should  be  specially  pre- 
pared to  leave  practically  no  ash.  Such  a  paper 
is  placed  in  a  glass  weighing-bottle,  heated  in  the 


SEWAGE  WORKS  ANALYSES.         105 

drying-oven  to  110°  C.,  cooled  in  a  desiccator* 
and  weighed,  then  reheated  and  weighed  again 
till  constant.  The  same  operation  of  drying, 
reheating,  and  reweighing  till  constant  is  repeated 
after  the  suspended  matter  has  been  collected  on 
the  filter. 

Examples : — 

Quantity  of  sample  (raw  sewage)  taken  =  210  c.c. 
Weight  of  bottle  +  filter  paper 

+  suspended  matter  =  10-5044  grms. 

Weight  of  bottle  +  filter  paper        =  io'4345  grms. 

Weight  of  suspended  matter  =     -0699  grms. 

•0699  grm.  in  210  c.c.  =  '0233  grm.  in  70  c.c. 

=  23*3  grains  per  gallon 

2  '•?*  3 

=  -f-^  =  33'3  parts  per  100,000  total  suspended 

matter. 

The  filter-paper  and   suspended   matter  were 
ignited  in  a  platinum  crucible,  the  weight  being 
as  follows : — 
Weight  of  crucible  +  residue  after 

heating          ....  =29*6790  grms. 
Weight  of  crucible       .         .         .  =29*6392  grms. 
Mineral  residue,  after  heating      .  =     -0368  grms. 
•0368  grm.  in  210  c.c.  =  '0123  grm.  in  70  c.c. 
=  I2'3  grains  per  gallon. 

12*3          r 
=  —r^  =  17*6  parts  per  100,000 

of  mineral  matter. 

*  For  this  purpose  a  bell-jar,  under  which  is  placed  a 
small  dish  of  strong  sulphuric  acid,  may  be  used. 


106        SEWAGE   WORKS   ANALYSES. 

The  organic  or  volatile  matter  present  will  be 
represented  by  the  difference  between  these  two 
values : — 

23*3  — 12*3  =  11*0  grains  per  gallon. 
33*3  — 17*6  =  157  parts  per  100,000. 

To  save  time,  a  number  of  filter-papers  may  be 
dried  in  a  bottle  in  the  drying-oven  at  once,  and  a 
single  paper  used  as  required. 

When  the  sample  contains  a  large  amount  of 
suspended  matter,  e.g.,  in  storm-water,  a  suffi- 
ciently accurate  determination  may  be  made  by 
allowing,  say,  700  c.c.  of  the  sample  to  stand, 
when  the  greater  part  of  the  suspended  matter  will 
settle  out.  The  fairly-clear  liquid  may  be  syphoned 
off,  and  the  deposit  washed  on  to  a  smooth  tough- 
ened filter-paper  (e.g.,  Schleicher  and  Schiill,  No. 
575) »  washed  and  dried  in  the  air-bath  at  100°  to 
110°  C.  After  drying,  the  suspended  matter  can 
be  scraped  off  the  smooth  paper  into  a  weighed 
crucible  and  weighed.  On  igniting,  moistening 
with  ammonium  carbonate,  and  reheating,  the 
proportion  of  mineral  matter  may  be  obtained  as 
before. 

Where  a  large  number  of  determinations  have 
to  be  made,  they  may  be  much  facilitated  by 
the  use  of  a  centrifugal  machine.  There  are 
many  types  of  these,  all  depending  on  the  fact 
that  if  a  solution  containing  suspended  particles 
is  rapidly  whirled  round,  the  particles  tend  to 
collect  at  the  bottom  of  the  liquid  if  they  are 


FIG.  7.— CENTRIFUGE    FOR    DETERMINING 
SUSPENDED    MATTERS. 


[To  face  page  107. 


SEWAGE   WORKS   ANALYSES.         107 

heavier  than  the  latter,  at  the  top  if  they  are 
lighter. 

A  convenient  form  of  centrifugal  machine  is 
shown  in  Fig.  7.  It  is  known  as  the  High-speed 
Medical  Centrifuge,  and  consists  essentially  of 
two  tapering  aluminium  tubes  swinging  loosely  at 
each  end  of  a  horizontal  metal  support  attached 
at  the  centre  to  a  vertical  rod,  which  can  be 
rapidly  rotated  on  turning  the  handle,  actuating 
the  mechanism  within  the  instrument.  Glass 
tubes  to  contain  about  10  c.c.  of  the  sample  to  be 
tested  are  provided  with  the  instrument  to  fit  into 
the  aluminium  tubes. 

On  turning  the  handle,  the  aluminium  tubes, 
with  their  contents,  swing  into  a  horizontal  posi- 
tion, and  can  be  whirled  round  at  the  rate  of 
2,500  revolutions  per  second. 

The  operator  should  be  protected  by  a  wire 
screen  round  the  instrument,  in  case  the  alumi- 
nium tubes  and  their  horizontal  support  should 
become  detached  during  the  whirling  operation. 

After  a  few  minutes'  whirling  all  the  suspended 
matter  in  the  sample  will  be  found  collected  at 
the  apex  of  the  glass  tube. 

It  is  well  to  fix  an  indiarubber  ring  round  the 
vertical  pillar,  to  prevent  jarring  of  the  aluminium 
tubes  against  the  pillar  as  the  machine  is  brought 
to  a  standstill. 

The  amount  of  liquid  which  can  be  whirled  at 
once  in  the  machine  is  limited,  but  as  the  whirl- 
ing operation  takes  but  a  short  time,  the  clear 


io8        SEWAGE  WORKS  ANALYSES. 

liquid  can  be  poured  off  from  the  deposited 
matter,  a  fresh  quantity  added,  and  the  whirling 
repeated. 

By  using  graduated  tubes  an  approximate  idea 
of  the  quantity  of  suspended  matter  present  can 
be  obtained  by  simply  noting  the  volume  of  the 
deposit  in  different  cases,  but  as  this  depends  on 
the  character  of  the  suspended  matter,  whether 
light  or  heavy,  and  on  the  amount  of  whirling 
and  consequent  compression  to  which  it  has 
been  subjected,  it  is  better  to  actually  weigh  the 
deposit. 

This  can  be  done  with  sufficient  accuracy  by 
pouring  off  the  liquid  in  the  tube,  adding  a  few 
drops  of  distilled  water,  and  stirring  with  a  plati- 
num wire  to  loosen  the  deposit,  then  transferring 
this  to  a  weighed  crucible,  carefully  evaporating 
off  the  small  amount  of  water  in  the  air-bath  at 
100°  to  110°  C.,  cooling  in  the  desiccator,  and 
weighing. 

The  amount  of  mineral  matter  in  the  deposit 
can  be  determined  as  before. 

Determination  of  the  Total  Solids  in  a  Tank. — It 
is  often  of  great  interest  and  importance  to  deter- 
mine, as  exactly  as  possible,  the  actual  quantity 
of  solid  matter  present,  either  in  a  sedimentation 
or  septic  tank. 

This  can  be  accomplished  with  a  fair  amount  of 
accuracy  by  the  use  of  the  dipping  tube,  shown  in 
Fig.  8,  by  which  a  section  of  the  tank  can  be  with- 
drawn and  examined. 


SEWAGE  WORKS  ANALYSES.        109 

The  tube,  whose  length  depends  upon 
the  depth  of  water  in  the  tank,  is 
conveniently  made  in  sections  joined  by 
an  indiarubber  band,  the  free-ends  being 
protected  by  brass  collars,  the  whole 
being  mounted  on  a  strong  board  which 
is  marked  at  intervals  of  six  inches. 
Through  the  length  of  the  tube  a  stout 
string  passes,  which  is  attached  at  the 
lower  end  of  the  tube  to  an  indiarubber 
ball.  By  pulling  the  string  tightly  the 
ball  closes  the  lower  end  of  the  tube. 
The  string  can  then  be  fixed  to  a 
nail  driven  into  the  upper  end  of  the 
board. 

In  order  to  obtain  a  section  of  the 
tank,  the  tube  is  slowly  and  carefully 
lowered  to  the  bottom,  the  ball  and 
string  being  kept  loose.  The  level  of 
the  water  inside  and  outside  the  tube 
should  be  as  nearly  as  possible  the 
same  throughout  the  operation,  or  the 
section  will  not  be  a  true  one.  When 
the  tube  has  reached  the  bottom  of  the 
tank,  it  should  be  raised  just  sufficiently 
to  enable  the  ball  to  be  pulled  tightly 
over  the  lower  end.  The  string  is  then 
fixed  and  the  tube  drawn  up.  There 
should  be  no  escape  of  water  at  the 
bottom  of  the  tube.  After  allowing  _ 
a  few  minutes  for  settlement,  the  level 


i  io        SEWAGE   WORKS  ANALYSES. 

of  the  sludge  in  the  tube  may  be  read,  and  the 
contents  emptied  into  a  pail  from  which,  after 
stirring,  a  sample  may  be  drawn. 

Similar  sections  should  be  taken  at  various 
points  round  the  tank  in  order  to  obtain  an 
average.  The  total  solids,  both  mineral  and 
volatile,  per  gallon  of  the  mixed  sample  thus 
obtained  can  then  be  determined  by  any  of  the 
above  methods. 

Knowing  the  capacity  of  the  tank  in  gallons, 
the  total  solids  present  in  it  can  be  calculated. 

Example : — 

A  section,  taken  in  the  above  manner,  of  the 
open  septic  tank  in  Manchester  was  found  to 
contain  3624*6  grains  of  solid  matter  per  gallon. 
As  15*68  grains  per  gallon  is  equivalent  to  i  ton 
per  million  gallons,  3624*6  grains  per  gallon  will 
be  equivalent  to  231*2  tons  per  million  gallons. 
As  the  capacity  of  the  tank  was  1,125,000  gallons, 
the  amount  of  suspended  matter  contained  in  it 
was  260  tons. 

Determination  of  Composition  of  Sludge. — Such  a 
determination  as  above  described  gives  the  actual 
amount  of  solid  matter  in  the  tank,  assuming  that 
the  latter  could  be  obtained  in  a  dry  state. 

The  actual  amount  of  wet  sludge  depends,  as 
explained  on  p.  12,  on  its  density ;  and  it  is 
important,  therefore,  to  determine  the  percentage 
of  water  contained  in  the  sludge. 

This  can  be  done  with  sufficient  accuracy  by 
evaporating  down  about  200  grams,  of  an  average 


SEWAGE   WORKS  ANALYSES.         in 

sample  in  a  weighed  porcelain  dish,  drying 
in  an  air-bath  at  100°  to  110°  C.,  cooling  and 
reweighing. 

The    loss    of    weight    represents    the    water 
present. 


ii2         SEWAGE  WORKS   ANALYSES. 


CHAPTER   VIII. 

THE  ANALYSIS  OF  GASES  FROM  THE 
SEPTIC  TANK  AND  FROM  BACTERIAL 
FILTERS. 

THE  analysis  from  time  to  time  of  the  gases 
given  off  from  the  septic  tank,  or  of  those  present 
in  the  interstices  of  bacterial  niters,  affords  valu- 
able information  as  to  the  respective  processes. 

GASES  EVOLVED  FROM  THE  SEPTIC  TANK. 

The  changes  which  go  on  in  the  septic  tank  are 
not  yet  perfectly  understood,  the  proportion  of  the 
gases  evolved  varying  according  to  the  conditions 
in  the  tank  (see  Chap.  I.).  The  gases  for  the 
most  part,  however,  consist  of  marsh-gas  (methane 
CH4),  hydrogen  (H),  carbon  dioxide  (CO2),  and 
nitrogen  (N),  resulting  from  the  decomposition  of 
nitrogenous  organic  matter  and  cellulose. 

A  possible  decomposition  of  albumen,  resulting 
in  the  formation  of  marsh-gas,  etc.,  is  given  in  the 
following  equation  :  — 


+  4H. 
Cellulose  is  known  to   be  decomposed  by  an 


SEWAGE   WORKS  ANALYSES.         113 

organism  bacillus  amylobacter,  partly  at  any  rate, 
according  to  the  following  equations : — 

C6H10O5  +  H2  O  =  C6Hi2O6. 

C6Hi2O6=3CO2+3CH4. 

GASES   PRESENT   IN   THE   INTERSTICES  OF 
BACTERIAL   FILTERS. 

The  changes  taking  place  in  the  bacterial  filters 
are  chiefly  of  the  nature  of  combustion,  and  for  this 
to  take  place  to  the  best  advantage  there  should,  of 
course,  be  an  adequate  supply  of  oxygen  present. 

Some  nitrogen  may  be  evolved  from  denitrifica- 
tion  changes,  such  as  have  been  described  on  p.  62, 
which  will  lessen  the  proportion  of  oxygen  in  the 
interstices  of  the  bed. 

The  analysis  of  air  drawn  from  the  interior  of 
a  contact  bed  during  rest,  or  from  a  continuous 
filter  at  any  time,  will  show  the  state  of  aeration 
at  various  depths.  If  the  proportion  of  carbonic 
acid  present  in  such  a  bed  is  excessive,  and  at  the 
same  time  but  little  oxygen  is  found,  a  period  of 
rest  is  evidently  necessary. 

METHOD   OF  COLLECTING   SAMPLES. — GAS   FROM 
SEPTIC   TANKS. 

The  gas  may  be  collected  from  either  the  open 
or  closed  septic  tank  by  means  of  a  bottle  provided 
with  an  indiarubber  stopper  with  two  holes. 
Through  one  of  these  a  glass  tube,  A,  passes  to 
the  bottom,  through  the  other  a  second  tube,  B, 
passes  just  beyond  the  stopper  (see  Fig.  9).  A 

s.w.  i 


1 14        SEWAGE  WORKS  ANALYSES. 

piece  of  indiarubber  tubing  and  a  pinch-cock  serve 
to  close  each  tube. 

To  collect  a  sample  of  gas  from  the  open  tank, 
the  bottle  is  filled  with  water,  and  the  longer  of 
the  two  tubes,  A,  is  joined  to  a  funnel  which  dips 
below  the  surface  of  the  water  in  the  tank.  The 
exit  tube,  B,  of  the  bottle  should  also  be  brought 
beneath  the  water  level.  Both  pinch-cocks  are 
then  opened,  and  if  the  sludge  below  the  bottle  is 
stirred,  enough  gas  will  quickly  be  evolved  to  fill 
the  bottle,  the  water  escaping  by  the  short  tube. 
When  the  bottle  is  full  of  gas  the  pinch-cocks  are 
closed  while  the  bottle  is  still  immersed,  and  the 
sample  is  brought  into  the  laboratory  for  analysis.* 

The  same  arrangement  may  be  used  for  the 
closed  tank,  the  longer  tube  being  attached  to  a 
vent  tap  in  the  roof  instead  of  to  a  funnel.  In 
order  to  collect  a  sample  of  gas  the  exit  valve 
of  the  tank  should  be  closed  and  the  sewage 
headed  up  in  the  tank,  thus  creating  a  pressure 
which  forces  the  gas  into  the  bottle. 

GASES  FROM  BACTERIA  BEDS. 

To  collect  the  gases  from  bacteria  beds  a  narrow 
iron  tube  (J-inch  internal  diameter)  is  hammered 
into  the  bed  to  any  desired  depth.  In  order 
to  prevent  chokage  of  the  end  of  the  tube  as 
it  enters  the  bed,  a  small  cork  is  inserted  which 

*  The  rate  of  evolution  of  gas  from  an  open  septic  tank 
may  be  determined,  and  the  collection  of  samples  facilitated, 
by  the  provision  of  a  small  sheet  iron  gas-holder,  which  can 
be  suspended  at  different  points  along  the  margin  of  the  tank. 


FIG.  9. 


[  To  face  page  114. 


:>SITY   3 


VERSiTY 

OF 


A 


FIG.  10. 


\ToJace  page  115. 


SEWAGE  WORKS  ANALYSES.        115 

is  afterwards  knocked  out,  while  the  tube  is  still  in 
position,  by  means  of  an  iron  rod  inserted  in  the 
tube  and  hammered  at  the  upper  end. 

The  gases  may  then  be  drawn  from  the  bed 
in  a  way  somewhat  similar  to  that  by  which  they 
are  obtained  from  the  septic  tank. 

The  arrangement  is  shown  in  Fig.  10.  The  upper 
end  of  the  iron  tube  C  is  fitted  with  an  indiarubber 
stopper  through  which  passes  a  narrow  glass  tube. 
The  sampling  apparatus  is  joined  by  an  india- 
rubber  connection,  D,  to  the  end  of  this  tube.  This 
connection  can  be  closed  by  a  pinch-cock.  All 
connections  must  be  air-tight  to  ensure  that  the 
gas  is  actually  drawn  from  the  bed  at  the  depth 
reached  by  the  iron  tube. 

In  collecting  samples  of  gas  from  bacterial  filters 
it  is  necessary  to  reject  the  first  portions  with- 
drawn, as  they  are  likely  only  to  represent  the  gas 
within,  or  immediately  surrounding,  the  iron  tube. 
It  is  convenient,  therefore,  to  use  two  bottles 
connected  up  as  in  Fig.  3.  The  smaller  bottle,  A, 
may  have  a  capacity  of  8  oz.,  a  half  Winchester 
may  be  used  for  the  larger  bottle,  B.  To  obtain 
a  sample,  both  bottles  are  filled  with  water,  the 
stoppers  and  tubes  inserted  and  the  pinch-cocks 
closed.  Connection  is  then  made  with  the  bed  at 
D  without  opening  the  pinch-cocks.  The  pinch- 
cocks  E  and  F  are  then  opened,  and  finally  the 
pinch-cock  D.  The  water  flows  away  through  F, 
and  the  gas  from  the  bed  is  withdrawn  through 
the  sample  bottle  A.  When  the  bottle  B  is 

I  2 


n6        SEWAGE  WORKS  ANALYSES. 

nearly  empty  all  the  pinch-cocks  are  closed,  and 
A  is  removed  for  analysis  of  its  contents. 

By  using  only  the  one  small  bottle  A  for  col- 
lecting the  gas  the  operation  can  be  carried  out 
by  one  manipulator,  but  in  this  case,  when  the 
bottle  is  nearly  empty,  the  end  of  the  iron  tube 
must  be  closed  by  the  pinch-cock  D  and  the 
bottle  A  removed,  refilled  with  water,  and  at 
least  one  other  collection  of  gas  made  before  it 
is  safe  to  assume  that  a  true  sample  has  been 
obtained. 

In  drawing  samples  of  gas  from  continuous 
filters,  the  iron  tube  may  be  inserted  laterally, 
and  the  glass  connection  to  the  sampling  bottles 
bent  at  right  angles  so  that  the  bottles  may  still 
be  held  vertically. 

ANALYSIS  OF  THE   GASES. 

General  Description  of  the  Method. — Septic  Tank 
Gases. — These  consist  for  the  most  part  of  methane 
or  marsh-gas  (CH4),  hydrogen  (H),  carbon  dioxide 
(CO3),  and  nitrogen  (N). 

The  carbon  dioxide  is  determined  by  noting  the 
amount  of  gas  absorbed  by  potash  from  a  given 
volume  of  the  sample. 

The  marsh-gas  and  hydrogen  are  determined 
by  exploding  the  volume  of  the  sample  remaining 
after  removing  carbon  dioxide  with  excess  of 
oxygen,  noting  the  contraction  in  volume  after 
explosion  and  measuring,  by  potash  absorption, 
the  amount  of  carbonic  acid  produced. 


P 

\ 

UNIVERSITY 

OF 


i!^ 


FIG.  ii.— APPARATUS   FOR   GAS   ANALYSIS. 


[To  face  page  117. 


SEWAGE   WORKS   ANALYSES.         117 

From  these  data  the  percentages  of  hydrogen 
and  marsh-gas  can  be  calculated. 

Gases  from  Bacteria  Beds. — In  this  case  it  is 
important  to  determine  the  percentage  of  carbon 
dioxide  and  of  oxygen. 

The  carbon  dioxide  is  determined  by  potash 
absorption  as  above  mentioned.  Afterwards  the 
oxygen  in  the  same  sample  is  absorbed  by  potas- 
sium pyrogallate  and  the  decrease  in  volume  noted. 
The  residual  gas,  after  removing  the  oxygen  and 
carbon  dioxide,  is  assumed  to  be  nitrogen. 

Apparatus  and  Reagents. — In  order  to  analyse  the 
gases  thus  obtained,  a  modified  form  of  Orsat's 
gas  analysis  apparatus  will  be  found  convenient 
(see  Fig.  n). 

A  is  a  graduated  cylinder  surrounded  by  a  water 
jacket,  provided  with  platinum  wires  for  sparking, 
and  connected  with  a  mercury  reservoir,  F,  and  a 
narrow  levelling  tube  G.  B,  C,  D  are  cylinders  for 
absorption  reagents,  containing  lengths  of  narrow 
glass  tubing  to  form  a  large  surface  on  which  the 
absorption  of  gas  by  the  reagent  can  take  place. 
B  contains  strong  potash  solution  ;  C  and  D 
contain  alkaline  pyrogallate. 

The  solutions  are  made  up  as  follows : — 

Potash  solution.-—  240  grms.  stick  potash  are 
dissolved  in  i  litre  of  water. 

Alkaline  Pyrogallate. — As  this  solution  cannot, 
of  course,  be  kept  exposed  to  the  air,  as  it  rapidly 
absorbs  oxygen,  enough  only  should  be  made  up  at 
one  time  to  fill  one  of  the  two  pipettes,  C  and  D. 


u8        SEWAGE   WORKS  ANALYSES. 

Each  pipette  holds  about  200  c.c.  The  solution 
is  therefore  made  by  dissolving  40  grms.  of  pyro- 
gallic  acid  in  200  c.c.  of  the  above  potash  solution. 

Battery  and  Coil. — The  sparking  apparatus  con- 
sists of  a  single  bichromate  cell  and  a  Ruhmkorff 
coil  capable  of  giving  J  inch  spark. 

The  bichromate  cell  is  of  about  i  litre  capacity. 
It  is  charged  with  600  c.c.  of  water,  200  c.c.  of 
concentrated  sulphuric  acid,  and  100  grms.  of 
potassium  bichromate.  The  solution  should  be 
made  in  a  separate  vessel,  e.g.,  a  litre  flask.  The 
bichromate  is  first  dissolved  in  the  water  and  the 
acid  is  added  carefully  ;  the  mixture  is  allowed  to 
cool  before  being  put  into  the  cell. 

Oxygen. — A  supply  of  oxygen  is  also  required 
when  analyses  of  the  gases  from  the  septic  tank 
have  to  be  made. 

Enough  for  a  number  of  determinations  can  be 
made  by  heating  a  mixture  of  potassium  chlorate 
and  manganese  dioxide  (i  part  MnO2,  6  KC1O8)  in 
a  flask,  rejecting  the  first  portion  of  gas  evolved, 
and  collecting  a  litre  flask  full  over  water. 

The  flask  when  full  is  closed  while  under  water 
with  a  double  bored  indiarubber  stopper,  through 
one  hole  of  which  is  passed  the  stem  of  a  tap 
funnel,  and  through  the  other  a  delivery  tube  bent 
at  right  angles  and  closed  by  a  piece  of  indiarubber 
tubing  and  a  pinch-cock.  By  opening  the  pinch- 
cock  and  allowing  water  to  run  through  the  tap 
funnel,  the  oxygen  can  be  driven  out  of  the  flask 
as  required. 


SEWAGE   WORKS  ANALYSES.         119 

In  order  to  free  the  oxygen  from  any  traces  of 
carbon  dioxide  or  chlorine  which  may  have  come 
over  from  the  manganese  dioxide  and  chlorate,  a 
little  caustic  soda  solution  should  be  introduced 
into  the  flask  from  the  tap  funnel  (care  being  taken 
that  none  finds  its  way  into  the  exit  tube  of  the 
flask),  and  the  oxygen  left  in  contact  with  the 
solution  over  night  before  use. 

ANALYSIS  .OF   SEPTIC   TANK   GASES. 

To  carry  out  the  analysis  of  a  sample  of  the  gases 
collected  in  the  manner  described,  the  shorter  tube 
of  the  bottle  containing  the  sample  is  attached  to 
the  apparatus  at  E,  the  taps  to  the  reagent  cylinders 
being  closed  and  the  graduated  tube  and  capillary 
tube  full  of  mercury. 

The  longer  tube  of  the  bottle  is  attached  by  an 
indiarubber  junction  to  a  tube  full  of  water  dipping 
into  a  beaker  of  water.  On  opening  the  screw 
clips  and  lowering  the  mercury  in  the  graduated 
tube,  or  eudiometer,  of  the  Orsat  apparatus,  any 
desired  quantity  of  gas  can  be  drawn  into  the 
eudiometer.  At  the  same  time  water  enters  the 
bottle  from  the  beaker  to  take  the  place  of  the  gas. 
Not  more  than  20  c.c.  should  be  taken  for  a  com- 
plete analysis.  Before  noting  the  volume  of  gas 
taken,  the  mercury  should  be  adjusted  to  as 
nearly  as  possible  the  same  level  in  the  eudiometer 
and  the  open  levelling  tube.  The  taps  and  pinch- 
cocks  may  then  be  closed  and  the  sample  bottle 
removed. 

The  carbonic  acid  present  is  first  determined 


120        SEWAGE  WORKS  ANALYSES. 

by  opening  the  tap  connected  with  the  potash 
cylinder,  and  by  raising  the  mercury  reservoir, 
carefully  passing  the  gas  sample  into  the  potash 
cylinder. 

The  gas  should  be  allowed  to  stand  in  contact 
with  the  potash  for  five  minutes,  and  then  returned 
to  the  eudiometer  and  the  volume  remeasured, 
care  being  taken  to  level  the  mercury  as  before. 

This  process  should  be  repeated  till  the  volume 
of  the  gas  remains  constant.  A  volume  of  oxygen 
should  now  be  added  from  the  oxygen  flask  equal 
to  more  than  twice  the  volume  of  the  gas  taken, 
i.e.,  if  20  c.c.  of  gas  have  been  taken,  at  least 
60  c.c.  of  oxygen  must  be  added,  or  the  combustion 
on  subsequent  explosion  will  be  incomplete. 

The  oxygen  is  added  simply  by  joining  the  exit 
tube  of  the  oxygen  flask  to  the  apparatus  and 
running  in  water  from  the  tap  funnel  carefully, 
the  mercury  reservoir  being  simultaneously  lowered 
until  the  requisite  quantity  of  oxygen  has  been 
sent  into  the  apparatus.  The  volume  of  the  gas 
and  oxygen  is  now  measured,  the  pinch-cock  and 
tap  at  the  inlet  being  closed.  The  mercury 
reservoir  is  now  lowered  till  the  level  outside 
the  eudiometer  is  slightly  lower  than  the  level 
inside.  The  bottom  tap  of  the  eudiometer  is  then 
closed. 

The  mixture  is  now  sparked  from  the  bichromate 
battery  and  coil.  •  The  operator  should  be  pro- 
tected by  a  screen  when  the  spark  passes,  in  case 
of  accident. 


SEWAGE  WORKS  ANALYSES.        121 

The  tap  communicating  with  the  mercury  reser- 
voir is  now  opened  and  the  gas  allowed  to  cool  for 
about  ten  minutes,  when  another  reading  is  taken. 
Further  readings  should  be  taken  at  intervals  of 
five  minutes  until  no  further  contraction  is 
observed,  the  volume  being  then  carefully  re- 
corded. The  difference  between  this  volume  and 
that  of  the  mixed  gases  is  the  contraction  on  explo- 
sion. The  gas  in  the  eudiometer  is  now  passed 
into  the  potash  tube  by  opening  the  corresponding 
tap  and  raising  the  mercury  reservoir. 

When  all  the  gas  is  passed  over,  the  tap  may 
be  closed  and  the  mercury  reservoir  lowered.  On 
opening  the  tap  the  gas  passes  back  into  the 
eudiometer  and  may  be  again  measured.  The 
contact  with  potash  should  be  repeated  until  the 
volume  is  constant.  The  volume  absorbed  repre- 
sents the  carbon  dioxide  formed  on  explosion. 

These  measurements  are  really  sufficient  to 
determine  the  composition  of  the  gas,  but  it  is 
useful,  as  a  check,  to  pass  the  residual  gases  into 
alkaline  pyrogallate  solution,  measuring  the  absorp- 
tion and  repeating  the  contact  till  the  volume  is 
constant  as  before.  The  volume  absorbed  equals 
the  volume  of  residual  oxygen. 

The  following  data  are  then  available  given  in 
the  order  in  which  they  are  determined  : — 

a.  Original  volume  of  gas  taken. 

b.  Volume  after  absorption  of  CO2  by  potash. 

c.  Volume  of  gas  after  addition  of  oxygen. 

d.  Volume  of  gas  after  explosion. 


122         SEWAGE  WORKS  ANALYSES. 

e.  Volume  of  gas  after  explosion  and  contact 
with  potash. 

/.  Volume  of  gas  after  contact  with  alkaline 
pyrogallate. 

From  these  data  the  composition  of  the  gas 
can  be  calculated  as  follows  :  — 

a  —  b  =  volume  of  carbon  dioxide. 

c  —  d  =  contraction  on  explosion. 

d—e  =  volume  of  carbon  dioxide  produced  by 
explosion. 

e—  /  =  volume  of  residual  oxygen. 

The  volume  of  carbon  dioxide  produced  by  the 
explosion  is  equal  to  the  volume  of  marsh-gas 
(methane)  present  in  the  original  sample,  as  is 
seen  by  the  following  equation  :  — 


i  vol.  2  vols.  I  vol.        (steam  condensed). 

From  this  equation  it  is  also  seen  that  the 
combustion  of  the  marsh-gas  is  responsible  for  a 
contraction  after  explosion  equal  to  twice  its  own 
volume. 

Any  further  contraction  must,  therefore,  be  due 
to  combustion  of  hydrogen  (unless  other  gases 
such  as  ethylene  (C2H4)  or  carbonic  oxide  (CO) 
are  present,  and  this  has  not  been  found  to  be 
the  case).  Of  this  further  contraction  two-thirds 
represent  the  volume  of  the  hydrogen,  thus  :  — 

H2+0  =  H20. 
2  vols.  i  vol.     (condensed  to  liquid). 

The  volume  of  the  methane,  therefore,  will  be 
d  —  e  =  x. 


SEWAGE  WORKS  ANALYSES,         123 


The  volume  of  the  hydrogen  will  be2(c  —  ^— 2x). 

3 

The  following  example  obtained  in  practice  will 
illustrate  the  method  of  calculating  the  results. 

The  eudiometer  being  graduated  from  the 
bottom,  the  volumes  corresponding  to  the  read- 
ings are  obtained  by  subtracting  the  latter  from 
100. 


Reading. 

Volume  =100 
-  Reading. 

Volume  of  gas  taken 

=  a 

82*2 

I7'8 

Volume  of  gas  after  contact 

with  potash 

=  b 

83'4 

16-6 

Volume  of  gas  after  addition  of 

oxygen 

=  c 

21'2 

78-8 

Volume  of  gas  after  explosion 
Volume  of  gas  after  explosion 

47*2 

52-8 

and  cooling 

=  d 

50-2 

49-8 

Volume  of  gas  after  contact 

with  potash 

=  e 

63-8 

36-2 

Volume  of  carbon  dioxide  present  =  a  —  b=    1*2 

Contraction  on  explosion  =  c  —  d  =  29*0 

Volume  of  carbon  dioxide  produced 
by  explosion  =  d— e  =  13*6 

i.e.,  volume  of  marsh-gas. 

The  contraction  on  explosion  due  to  the  marsh- 
gas  will  be  27*2  (i.e.,  twice  13*6) . 

The  contraction  on  explosion  due  to  hydrogen 
will,  therefore,  be  29*0  — 27*2  =  r8. 

The  volume  of  hydrogen  present  will,  therefore, 

be  r8x2  =  ra. 


i24        SEWAGE   WORKS   ANALYSES. 


1   2    A    XUU 

=    675 

"76*  4ft 

I7-8 

i7'8 

1*2  X   100 

/U   ^U 
=        675 

lO'IO 

17-8 

100*00 

These  volumes  are  calculated  to  percentages  as 
follows : — 

Percentage  of  CO3  = 
Percentage  of  CH4  = 

Percentage  of  H     = 

Percentage  of  N     = 

(by  difference)  

ANALYSIS  OF  GASES   FROM   BACTERIA   BEDS. 

This  analysis  of  the  gas  collected  from  the 
interstices  of  bacterial  filters  is  a  comparatively 
simple  operation.  From  70  to  100  c.c.  may  be 
measured  in  the  eudiometer  (as  described  on 
p.  119),  and  passed  first  into  the  potash  cylinder 
and  the  contraction  in  volume  noted.  This  should 
be  repeated  once  or  twice  till  no  further  change  in 
volume  occurs.  The  total  contraction  equals  the 
volume  of  carbon  dioxide  present. 

The  gas  is  then  similarly  subjected  to  the  action 
of  alkaline  pyrogallate.  The  contraction  in  volume 
equals  the  volume  of  oxygen  present. 

Any  residual  gas  may  be  assumed  to  be  nitrogen. 

Example : — 


Reading. 

Volume  =100 
-  Reading. 

Volume  of  gas  taken           
Volume  of  gas  after  contact  with 
potash         ...        ...        ...        ... 

I  r4 
I  Vd 

88-6 
86-6 

Volume  of  gas  after  contact  with 
alkaline  pyrogallate         

28-2 

7r8 

SEWAGE  WORKS  ANALYSES.         125 

Volume     of     carbon 

dioxide  present  =  88*6  — 86*6  =  2c.c. 
Volume  of  oxygen 

present  =  86'6  — 71*8  =  14*80.0. 

These  volumes  are  calculated  to  percentages  as 
follows : — 

Percentage  of  CO2  =    2*™  =  2*2  per  cent. 

oo'o 

~        14-8x100    T,- 
"          "    °  88^-'=l67        J> 

„   N      =  8n 

(by  difference)  loo'o 


126        SEWAGE   WORKS   ANALYSES. 


TABLE  I. 

THE  SYMBOLS  AND  ATOMIC  WEIGHTS  OF  THE 

ELEMENTS  MET  WITH  IN  SEWAGE  ANALYSIS. 

Element.  Symbol.  Atomic  Weight. 

Hydrogen  H       1*00 

Carbon  C       n'97  (12) 

Nitrogen  N       14*01  (14) 

Oxygen  O       15-96  (16) 

Sodium  Na  (Natrium)         23-00  (23) 

Magnesium  Mg 23-94  (24) 

Aluminium  Al      27*04  (27) 

Silicon...  Si       28-00  (28) 

Phosphorus  P        30-96  (31) 

Sulphur  S        31*98  (32) 

Chlorine  Cl      35-37  (35*5) 

Potassium  K  (Kalium) 39*03  (39) 

Calcium  Ca     39-91  (40) 

Chromium  Cr      52-45  (52*5) 

Manganese  Mn 54-80  (55) 

Iron     ...  Fe  (Ferrum)  55-88  (56) 

Zinc     ...  Zn ...  65*10  (65) 

Silver  ...  Ag  (Argentum)       107*66  (108) 

Mercury  Hg  (Hydrargyrum)           ...  199*80  (200) 


NOTE. — The  numbers  in  brackets  approximate  sufficiently  to 
the  exact  atomic  weights  to  be  used  without  sensible  error  in  the 
calculations  required  in  this  work. 


SEWAGE  WORKS  ANALYSES.         127 


TABLE  II. 

WEIGHTS  AND  MEASURES  OF  THE  METRIC 
SYSTEM. 

Weights. 

i  milligram  =  the  thousandth  part  of  i  gram,  or  o-ooi  gram, 

i  centigram  =  the  hundredth       ,,        ,,        ,,     ofoi  ",, 

i  decigram    =  the  tenth  ,,        ,,        ,,     0*1  ,, 

i  gram          =  the  weight  of  a  cubic  centimetre 

of  water  at  4°  C.  ro  ,, 

i  decagram  =  ten  grams.  10*0  ,, 

i  hectogram  =  one  hundred  grams.  ioofo  ,, 

i  kilogram    =  one  thousand    ,,  1000*0  ,, 

Measures  of  Capacity. 

i  millilitre  =       i    cubic  centimetre  or  the  measure  of 

i  gram,  of  water, 
i  centilitre  =     10  cubic  centimetres  or  the  measure  of 

TO  grams,  of  water. 
i  decilitre  =    100  cubic  centimetres  or  the  measure  of 

zoo  grams,  of  water, 
i  litre         =  1000  cubic  centimetres  or  the  measure  of 

1000  grams,  of  water. 

Measures  of  Length. 

i  millimetre  =  the   thousandth    part   of    one   metre    or 

o'ooi  metre. 
i  centimetre  =  the    hundredth   part    of    one    metre    or 

o'oi  metre, 
i  decimetre  =  the     tenth     part     of     one     metre     or 

ofi    metre, 
i  metre         =  the  ten-millionth  part  of  a  quarter  of  the 

meridian  of  the  earth. 


128        SEWAGE   WORKS  ANALYSES. 


TABLE  III. 
CONVERSION  TABLE. 


Quantity  per  Gallon. 

Quantity  in  One  Million 
Gallons. 

Parts  per  100,000. 

Grains. 

Cwts 

Lbs. 

•25 

0 

35-7I 

•36 

'50 

0 

71-42 

•71 

75 

O 

107-13 

I  -07 

i-oo 

I 

30-85 

1-42 

1-25 

I 

66-56 

1-79 

1-50 

I 

102-29 

2-14 

175 

2 

26-OO 

2-50 

2*00 

2 

61*71 

2-86 

2-25 

2 

97*42 

3*21 

2-50 

3 

21-14 

3'57 

2-75 

3 

56*85 

3'93 

3-00 

3 

92-57 

4-29 

3*25 

4 

16-28 

4-64 

3*50 

4 

52-00 

5'oo 

375 

4 

87-70 

5-36 

4-00 

5 

"'43 

5-71 

4]25 

5 

47-14 

6-07 

5 

82-85 

6-42 

475 

6 

6-56 

6-79 

5'oo 

6 

42-29 

7-14 

SEWAGE  WORKS   ANALYSES. 


129 


TABLE  IV. 

CONVERSION  TABLE  FOR  RECORDING  QUAN- 
TITY OF  SEWAGE  DEALT  WITH  PER  GIVEN 
AREA. 


Gallons  per  square 
yard. 

Gallons  per  acre. 

Cubic  metres  per  hectare 
(10,000  square  metres). 

IO 

48,400 

543*4 

15 

72,6oo 

815-1 

20 

96,800 

1086-8 

25 

I2I,OOO 

I358-5 

30 

145.200 

1630-2 

35 

169,400 

1901-9 

40 

193.600 

2173-6 

45 

217,800 

2445*3 

50 

242,000 

2717*0 

55 

266,2OO 

2988-7 

60 

290,400 

3260-4 

65 

3I4.600 

3532-1 

70 

338,800 

3803-8 

75 

363,000 

4075'5 

80 

387.200 

4347*2 

85 

411,400 

4618-9 

90 

435.600 

4890-6 

95 

459,800 

5162-3 

100 

484,000 

5434*0 

105 

508,200 

5705'7 

no 

532,400 

5977*4 

"5 

556,600 

6249-1 

1  20 

580,800 

6520-8 

125 

605,000 

6792-5 

130 

629,200 

7064-2 

135 

653.400 

7335*9 

140 

677,600 

7607-6 

145 

701,800 

7879-3 

150 

726,OOO 

8151-0 

155 

750,200 

8422-7 

1  60 

774,400 

8694-4 

s.w. 


130         SEWAGE   WORKS  ANALYSES. 


CONVERSION  TABLE— continued. 


Gallons  per  square 
yard. 

Gallons  per  acre. 

Cubic  metres  per  hectare 
(10,000  square  metres). 

I65 
170 

175 
.      180 

185 
190 

195 
200 

798,600 
833,800 
847,000 
871,300 
895,400 
919,600 
943,800 
968,000 

8966-1 

9237-8 

9509-5 
978l'2 
10052-9 
10324*6 
10596-3 
10868-0 

SEWAGE  WORKS  ANALYSES.        131 


USEFUL  DATA. 

i  ton  =  1,015  kilogrammes. 

Ib.  =  453*6  grammes. 

oz.  =  28*35  grammes. 

grain  =  '0648  grammes. 

gallon  =  4,544  cubic  centimetres. 

fluid  oz.  =  28*35  cubic  centimetres. 

acre  =  4046-7  square  metres. 

sq.  yard  =  -836  square  metres. 

cubic  foot  of  water  contains  6-228  gallons. 

gallon  of  water  weighs  10  Ibs. 
i  gallon  of  sludge,  90  per  cent,  moisture,  weighs  u  Ibs. 

(about). 
15-68  grains  per  gallon  =  i  ton  per  million  gallons. 


The  Septic  Tank  System  of  Sewage 
Treatment  is  the  best  and  most  -  * 
economical*  x  x  x  x  x  x  ^  x  „ 

As  now  laid  down  it  embodies  the 
improvements  suggested  by  six.  years' 
practical  experience.  «  *  * 


Over  180  Installations  to  date. 


THE   SEPTIC  TANK  SYNDICATE, 

LIMITED, 

EXETER 

AND   WESTMINSTER. 


INDEX. 


ABSORBED  Oxygen  See  Oxygen. 

Acidity  and  Alkalinity,  Deter- 
mination of,  89 

Alkaline  Pyrogallate,  117 

Alkalinic  Potassium  Perman- 
ganate, 42 

Alkalinity,  Free  and  Combined, 

93 

Ammonia,    Determination   of, 
38 

Albuminoid,  39,  53 

Free  and  Saline,  39,  52 

Organic,  40,  58 

Water,  Ammonia-free,  42 
Asparagin,  39 
Atomic  Weights  of  Elements, 

Table,  126 

Bacillus  Antylobacter,  113 
Bacteria  Beds,  Gases  from  : 

Analysis  of,  117 

Samples,  Method  of  collect- 
ing, 115 
Bacterial  Filters,  4 

Control  of,  14 

Gases  present  in,  113 
Bailey's  Sewage  Recorder,  5 
Biological  Processes,  3 

CARBONIC  Acid,  Free,  94 
Catchpits  and    Screens,    Effi- 
ciency of,  9 

Caustic  Soda,  Standard,  93 
Centrifugal  Machine,  106 
Chemical  Treatment,  2 

Control  of,  10 
Chlorine,  86 


Colorimeter,  Stokes',  50 
Combined  Alkalinity,  94 
Contact  Beds,  4 

Control  of,  14 

Sampling    Liquids  entering 

and  leaving,  9 
Continuous  Filters,  4 
Conversion  Table,  128,  129 

DATA,  Useful,  131 
Denitrification,  62 
Disposal  Processes,  2 
Dissolved  Oxygen   See  Oxygen, 

EFFLUENT,  Degree  of  Purity 

necessary  in,  17 
Elements,  Symbols  and  Atomic 

Weights,  Table,  126 

FERRIC  Iron,  97 

Ferrou's  Ammonium  Sulphate, 

96 

Ferrou's  Iron,  97 
Filters,  Continuous,  4,  14 
Filtration,  Mechanical,  2 
Flow  of  Sewage,  Gauging,  5 
Four  Hours'  Test,  Substances 

other  than  Domestic  Sewage 

indicated  by,  30 

GASES,  Analysis  of : 
Bacteria  Beds,  117 
Bacterial  Filters,  113 
Samples,  Methods  of  collect- 
ing, 113,  114 
Septic  Tank,  112,  116,  119 


134 


INDEX. 


Gauges  for  recording  Sewage 

Flow,  5 
Glycocoll,  38 
Griess-Ilosvay  Solution,  64 

HEARSON  Incubator,  35 
High-speed    Medical    Centri- 
fuge, 107 

INCUBATOR  Tests,  34 
Iodide  Potassium,  24 
Iron  Ammonium  Alum,  98 
Iron,  Determination  of,  95 

Ferric,  97 

Ferrou's,  96 

Suspension,  Iron  in,  96,  98 

KENT'S  Meter,  for  measuring 
Discharge  from  Filters,  7 

Kjeldahl  Method  of  deter- 
mining Organic  Ammonia,  58 

LEUCINE,  38 

MEASUREMENT  of 

Sludge  Production,  12 
Solutions,  26 

Measures  and  Weights  of  the 
Metric  System,  Table,  127 

Mechanical  Filtration,  2 

Meta-phenylene-diamine,  66 

Methyl-orange,  91 

Micro  coccus  Uvei,  38 

Mineral  Acid,  Free,  94 

NESSLERISATION,  40 
Nitric  Nitrogen,  71 
Nitrite,  Sodium,  66 
Nitrites    and    Nitrates,   deter- 
mining, 61 

ORGANIC  Ammonia,  40,  58 
Orsat's    Gas    Analysis   Appa- 
ratus, 117 

Oxygen,  Absorbed  : 
Determination  of,  21 
Four  Hours'  Test,  26 
Three  Minutes'  Test,  31 


Oxygen,  Dissolved,  Determina- 
tion of : 

Ramsay's  Method,  81 
Rate  of  Absorption,  82 
RoscoeandLunt'sMethod.Si 
Test  for,  20,  82 
Thresh's  Method,  75 


PALATINE  Company's  Record- 
ing Gauge,  5 

Permanganate  Alkaline  Potas- 
sium, 42 

Phenol-phthalein,  90 

Potash  Solution,  117 

Potassium  Solutions : 
Chromate,  87 
Iodide,  24 

Nitrite,  Standard,  63 
Permanganate,  23,  42 
Sulphocyanate,  98 

Purification  Processes,  3 

Purity  necessary  in  an  Effluent, 
Degree  of,  17 

Pyrogallate,  Alkaline,  117 

RAMSAY,  Prof.,  Method  of  de- 
termining Dissolved  Oxygen, 
81 

Results  of  Analysis,  recording, 

15 

SAMPLING,  Methods  of,  8,  113 

Screens  and  Catchpits,  Effi- 
ciency of,  10 

Septic  Tank  : 
Control  of,  12 

Gases  in,  Analysis,  112,  116 
Purification  Process,  3 

Silver  Nitrate,  Standard  Solu- 
tion, 87 

Sludge : 
Composition,    Determining 

no 
Production,  Measuring,  12 

Sodium  : 

Carbonate,  42 
Nitrite,  67 
Thiosulphate,  24,  76 


INDEX. 


Solids,  Determination  of: 

in  Solution,  101 

in  Suspension,  103 

Tank,  Total  of  Solids  in,  108 
Solutions,  Measurement  of,  26 
Starch  Solution,  24,  76 
Stokes'  Colorimeter,  50 
Sulphocyanate,  Potassium,  98 
Sulphuric  Acid,  23,  76,  96,  98 

Dilute,  66 

Standard,  91 
Symbols  of  Elements.Table,  126 


THREE  Minutes'  Oxygen  Ab- 
sorption Test,  31 

Thresh,  Dr. ,  Method  of  Deter- 
mining Dissolved  Oxygen,  75 

Treatment,  Chemical,  Control 
of,  10 

WATER,  Ammonia-free,  42 
Weights  and  Measures  of  the 

Metric  System,  Table,  127 
Workmen,     Use     of     Three 

Minutes'  Test  by,  32 


The  Self-acting  Triple  Tank  System  of 
Sewage  Treatment  by  Bacterial  Agency 

IS   THE   BEST   AND   MOST 
UP-TO-DATE. 

This  method  effects  a  saving  of  £91  per  annum  for  each 
100,000  gallons  of  sewage  treated  per  day,  as  compared 
with  chemical  treatment  and  the  labour  in  connection 
therewith.  

The  Self-acting  Triple  Automatic  Apparatus 
for  Filling  and  Emptying  Bacteria  Beds 

Can  be  attached  to  existing  works  at  low  cost. 
Automatic  and  reliable  in  their  working. 
No  cog-wheels  to  get  out  of  order. 
No  syphons  and  no  fear  of  blocking. 


ILLUSTRATED    PAMPHLET    POST    FREE. 

HALLER  &  MACHELL, 

Civil  Engineers,  DEWSBURY. 


FREDK.  JACKSON  &  CO., 

14,  Cross  Street, 

MANCHESTER. 


TELEGRAPHIC  ADDRESS:    APPARATUS,    MANCHESTER. 
TELEPHONE    No.    aoaa. 


JOT*  HL 


Balances, 
General  Chemical 
Apparatus,  and 

Pure  Chemicals, 

¥ 

Hempel,  Orsat, 

and  other 

GAS  ANALYSIS 
APPARATUS. 


Frederick  Jackson  &  Co. 
supply  the  various 
sections  of  Apparatus 
described  in  this 
work. 

Price  of  the  Apparatus  for  Gas  Analysis,  as  described  on 
page  117,  £3. 

Or  with  Battery,  Coil,  and  Connections,  complete,  £3  153. 


IUttiJrat*ir  JJri« 


fm  an  application. 


CHARLES  HEARSON  &  Co..  Ltd 

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Manufacturers    of  ... 


BIOLOGICAL 

EMBRYOL06KAL 

INCUBATORS, 

STERILIZERS,  AIR  PUMPS,  EMBEDDING  APPARATUS,  &c, 


Scientists   requiring   special   apparatus  for  Laboratory 

Work  should  avail  themselves  of  our  extensive  know- 

ledge   and    practical    experience    in    every  branch   of 

Physical  and  Mechanical  research. 


Address  for  full  particulars  : 

BIOLOGICAL    DEPARTMENT, 

235,    Regent  Street,    W., 
London,    England. 


Fitted  with 
l-in.,i-in 
and  ,',-in. 
(Oil-immer 
sion,  N.A. 
1.30)  Objec- 
tives, 
Circular 
Dust- 
proof 
Triple 
Nose- 
piece, 
Three 
Eye- 
pieces, 

Abbe  Condenser 
and  Case,  was 
supplied  to 
H.M.  Government 
for  the  work 
of  the  Royal 
Commission. 


Royal  Conjnjissioi) 

ON 

Sewage  Disposal. 


HENRY  CROUCH'S 

«  D.  P.  H." 

MICROSCOPE, 


THE    "  D.  P.  H."    MICROSCOPE. 

Full  Particulars  on  application  to 

HENRY    CROUCH, 

92,    Duncombe    Road,    LONDON,    N. 


MATHER  &  PLATT,  LD. 


PATENT  DISTRIBUTING  GEAR 

For  delivering  Sewage  to  Filter  Beds  in  regular  succession, 
in  measured  quantities,  or  at  regular  intervals. 

PATENT    RETAINING 

AND    DISCHARGING  VALVE 

For  "  holding  in  contact "  any  required  length  of  time. 

PATENT  REVOLVING  SPREADER 

(As  Illustrated  above). 

Reference,   on   application,    to   works  already  carried  out, 
and, appointments  for  seeing  the  same  in  operation. 


MATHER  &  PLATT,  LD. 

Mechanical,  Electrical,  and  Hydraulic  Engineers, 
Salford  Iron  Works,  MANCHESTER. 


<^.  Optical  Works,  JENA. 

Branches:  LONDON,  BERLIN,   FRANKFORT,  and   VIENNA. 


Microscopes  for  Bacteriological  Research. 

PHOTO- 

MICROGR3PHIC 
STflND. 


MODEL. 

With  wide  body- 
tube,  very  sensitive 
new  fine  adjust- 
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signed for  use  with 
our  Micro-planars, 
as  well  as  for 
Photography  with 
the  very  highest 
powers. 

It  can  also  be 
used  with  the  same 
facility  as  any 
other  Stand  for 
ordinary  visual 
observation. 


For  full  description  of  this,  and  of  our  Apochromatic 
Objectives  necessary  for  the  highest  class  of  Bacteriological 
Research,  see  NEW  CATALOGUE  OF  MICROSCOPES,  1902,  sent 
free  on  application  to  — 

CARL  ZEISS,  29,  Margaret  St.,  Regent  St.,  London,  W. 


SOME  REASONS  WHY 

ALDMINOFERRIC 

IS  SO  EXTENSIVELY  USED  FOR 

Sewage  Purification. 


It  is  the  best  and    most   economical 
cipitantt 

It    gives    a    clear,    colourless,    and 
putrescible  effluent, 

It    yields    a   less   weight    of    sludge    than 
any  other  precipitant, 

It    is   exceedingly    easy    to   use,   requiring 
scarcely  any  labour, 

And  "  holds  the  field  "  as  a  precipitant  after 
many  years'  practical  use* 


SOLE    MANUFACTURERS:- 


PETER  SPENCE  &  SONS, 

Manchester  Alum  Works, 

«^_.  MANCHESTER. 


THE 


STODDART 

CONTINUOUS  SEWAGE 

FILTER. 


The  Cheapest  and  most  Reliable  means  of  rendering 
Sewage  permanently  inoffensive. 

For  all  Particulars  apply  to    .    . 

F.  WALLIS   STODDART, 
Western     Counties'    Laboratory, 

BRISTOL. 


X 


ADAMS' 


PATENT    SEWAGE    LIFT   COY., 

(S.    H.   ADAMS,   A. M.I. C.E.I 

Engineering  Specialists  in  the  Manufacture 

of-  /-  - 

AUTOMATIC  APPARATUS  for 
BACTERIA  BEDS, 
CONTINUOUS  or 
INTERMITTENT  FILTERS,  &c, 

(Circular  up  to  £  acre,  Rectangular 
beyond — or  for  less), 

SEWAGE  PUMPING  Without  Cost, 
As  installed  for  .  .  . 

H.M.  WAR  OFFICE, 

„      BOARD   OF    WORKS, 
HOME  AND  FOREIGN  GOVERNMENTS, 
INSTITUTIONS,  MANSIONS,  &c. 

Amongst  others  the  Corporations  of— 

York,    Manchester,     Birmingham,    Croydon,    Epsom, 

Baling,  Sutton,   Newmarket,  St.  Albans,  Carlisle. 

GOLD    MEDAL,     PARIS,    &c. 

Works  :  London  Offices  : 

YORK,    ENGLAND.  7'    °LD  <2UEEN 

WESTMINSTER. 


THE    YORK    FILTER. 


UNIVERSITY  OF  CALIFORNIA  LIBRARY 
BERKELEY 


THIS  BOOK  IS  DUE  ON  THE  LAST  DATE 
STAMPED  BELOW 

Books  not  returned  on  time  are  subject  to  a  fine  of 
50c  r>er  volume  after  the  third  day  overdue,  increasing 
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demand  may  be  renewed  if  application  is  made  before 
expiration  of  loan  period. 


Mfeft  12  1918 


MAY   22  19?9 
.' 


1956  \M 


DS. 

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search. 


50m-7,'16 


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SORIES. 

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ES, 

LASSES, 
TU8,  &c. 

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IS. 


^tfv-t*' 


YbJ 


"VENTURI"   METER. 


For  Measuring  large  volumes 
of  Water  in  Trunk  or  other 
Mains. 

For  Filter  Bed  Regulation. 

For  Measuring  Sewage 
Effluents,  Slimes,   Etc. 


COMBINED  DIAPr 

Showing  rate? 
through  thp' 
with' 


_ECTRICAL  RECORDER. 

,  V  duplicating  the  "  Venturi"  Meter 

ecords  at  long  distances  from  the 

Meter  Tuba. 


VENTURI      MCTER     TUBE 

Full  descriptive  pamphlet  of  the  "Venturi"  Meter  sent  upon  application; 
also  to  those  interested,  a  Catalogue  of  G.  KENT'S  other  Water  Meters  and 
Water  Measuring  Appliances,  which  includes  the  "Absolute,"  "Uniform," 
Waste  Water,  and  Irrigation  Meters,  Rain  Gauge  Recorders,  Water  Level 
Indicators  and  Recorders,  Meter  Testing  Appliances,  Etc. 


G.  KENT, 

199,  200,  201,  HIGH  HOLBORN,  LONDON,  W.C. 


